Influence of finish line design on the marginal fit of nonprecious metal alloy coping fabricated by 3D printing, milling and casting using CAD-CAM / 대한치과보철학회지

Purpose@#The purpose of this study was to examine the correlation between the finish line designs and the marginal adaptation of nonprecious metal alloy coping produced by different digital manufacturing methods. @*Materials and methods@#Nonprecious metal alloy copings were made respectively from each master model with three different methods; SLS, milling and casting by computer aided design and computer aided manufacturing (CAD-CAM). Twelve copings were made by each method resulting in 72 copings in total. The measurement was conducted at 40 determined reference points along the circumferential margin with the confocal laser scanning microscope at magnification ×150. @*Results@#Mean values of marginal gap of laser sintered copings were 11.8 ± 7.4 μm for deep chamfer margin and 6.3 ± 3.5 μm for rounded shoulder margin and the difference between them was statistically significant (P < .0001). Mean values of marginal gap of casted copings were 18.8 ± 20.2 μm for deep chamfer margin and 33 ± 20.5 μm for rounded shoulder margin and the difference between them was significant (P = .0004). Conclusion: Within the limitation of this study, the following conclusions were drawn. 1. The variation of finish line design influences the marginal adaptation of laser sintered metal coping and casted metal coping. 2. Laser sintered copings with rounded shoulder margin had better marginal fit than deep chamfer margin. 3. Casted copings with deep chamfer margin had better marginal fit than rounded shoulder margin. 4. According to the manufacturing method, SLS system showed the best marginal fit among three different methods. Casting and milling method followed that in order.

Full mouth rehabilitation using 3D printed crowns and implant assisted removable partial denture for a crossed occlusion: a case report / 대한치과보철학회지

With the recent development of computer-aided design-computer-aided manufacturing technology and 3D printing technology, and the introduction of various digital techniques, the accuracy and efficiency of top-down definitive prosthetic restoration are increasing. In this clinical case, stable occlusion support was obtained through the placement of a total of 9 maxillary and mandibular posterior implants in patient with anterior-posterior crossed occlusion. The edentulous area of the maxillary anterior teeth, which showed a tendency of high resorption of the residual alveolar bone, was restored with a Kennedy Class IV implant assisted removable partial denture to restore soft tissue esthetics. Computed tomography guided surgery was used to place implants in the planned position, double scan technique was used to reflect the stabilized occlusion in the interim restoration stage to the definitive prostheses, and metal 3D printing was used to manufacture the coping and framework. This clinical case reports that efficient and predictable top-down full mouth rehabilitation was achieved using various digital technologies and techniques.

Effect of hemispherical dimples at titanium implant abutments for the retention of cemented crowns

PURPOSE@#. The aim of this study was to assess the effect of hemispherical dimple structures on the retention of cobalt–chromium (Co–Cr) crowns cemented to titanium abutments, with different heights and numbers of dimples on the axial walls. @*MATERIALS AND METHODS@#. 3.0-mm and 6.0-mm abutments (N = 180) and Co-Cr crowns were prepared. The experimental groups were divided into two and four dimple groups. The crowns were cemented by TempBond and PANAVIA F 2.0 cements. The retention forces were measured after thermal treatments. A twoway Analysis of Variance (ANOVA) and post-hoc Tukey HSD test were conducted to analyze change in retention forces by use of dimples between groups, as well as t test for the effect of abutment height change (α = .05). @*RESULTS@#. Results of the two-way ANOVA showed a statistically significant difference in retention force due to the use of dimples, regardless of the types of cements used (P < .001). A significantly higher mean retention forces were observed in the groups with dimples than in the control group, using the post hoc Tukey HSD test (P < .001). @*Results@#of t test displayed a statistically significant increase in the retention force with 6.0-mm abutments compared with 3.0-mm abutments (P < .001). The groups without dimples revealed adhesive failure of cements, while the groups with dimples showed mixed failure of cements. @*CONCLUSION@#. Use of hemispherical dimples was effective for increasing retention forces of cemented crowns.

Comparative study of surface characteristics and shear bond strength of 3D printed and milled 4Y-TZP / 대한치과재료학회지

This study aimed to compare the surface characteristics and the shear bond strength of veneering porcelain of 3D printed 4Y-TZP with milled 4Y-TZP. Thirty disks with 10 mm diameter and 1.2 mm thickness were fabricated. Fifteen were fabricated by 3D printing (Experimental group), and another 15 by milling (Control group). In each group, five were assigned to surface analysis. Surface roughness was measured using a confocal laser microscope. Surface energy was calculated by measuring the contact angles of water and diiodo-methane with a drop-shape analyzer. Another ten specimens were used to evaluate the shear bonding strength of veneering porcelain on the surface of 4Y-TZP. The surface of 3D-printed 4Y-TZP was very smooth, and the surface roughness (Ra, Rq) was significantly lower than that of milled 4Y-TZP (p<0.001). 3D-printed 4Y-TZP showed low wettability compared with milled 4Y-TZP, i.e., the water contact angle was significantly high (p=0.008), and the surface free energy was low (p=0.008). The shear bond strength to veneered porcelain of 3D printed 4Y-TZP was significantly lower than that of milled 4Y-TZP (p<0.001). The surface characteristics of 4Y-TZP were quite different by the manufacturing process. The smooth surface and low wettability of 3D-printed 4Y-TZP could affect its low shear bonding strength to veneering porcelain.

Full mouth rehabilitation of the patient with severely worn dentition and limited vertical dimension / 대한치과보철학회지

Severely worn dentition causes various complications such as loss of tooth structure, discoloration, pulp complications and loss of function and aesthetics. In this case, the patient showed particularly severe attrition in the anterior teeth and lack of space for restoration. The amount of vertical dimension was determined based on the diagnostic wax up, and the patient’s adaptation was evaluated by using a removable occlusal splint for 6 weeks. Thereafter, the coordination of the muscular nervous system, aesthetics, temporomandibular joint were re-evaluated for 3 months by restoring the fixed provisional restoration. Through the above treatment process, the final restoration was completed with full mouth fixed prosthesis using monolithic zirconia, and functionally and aesthetically stable results were obtained.

Comparative evaluation of two sets of complete dentures fabricated by digital and conventional workflow in a single patient: A case report / 대한치과보철학회지

Application of digital technology in dental treatments can simplify the treatment process and reduce patient discomfort. In regards of digital complete dentures, several commercial systems are available. However, these systems are not being routinely applied in Korea. In this case report, comparative analyses were performed regarding the two sets of complete dentures fabricated in digital and conventional workflow in a single patient. Complete dentures made with digital workflow were able to form an ideal occlusion because customized teeth were used. Compared to that, there were also limitations such as lower retention of mandibular dentures, so we would like to report this.

Comparative evaluation of two sets of complete dentures fabricated by digital and conventional workflow in a single patient: A case report / 대한치과보철학회지

Application of digital technology in dental treatments can simplify the treatment process and reduce patient discomfort. In regards of digital complete dentures, several commercial systems are available. However, these systems are not being routinely applied in Korea. In this case report, comparative analyses were performed regarding the two sets of complete dentures fabricated in digital and conventional workflow in a single patient. Complete dentures made with digital workflow were able to form an ideal occlusion because customized teeth were used. Compared to that, there were also limitations such as lower retention of mandibular dentures, so we would like to report this.

Restoration of implant-supported fixed dental prosthesis using the automatic abutment superimposition function of the intraoral scanner in partially edentulous patients / 대한치과보철학회지

The digital workflow of optical impressions by the intraoral scanner and CADCAM manufacture of dental prostheses is actively developing. The complex process of traditional impression taking, definite cast fabrication, wax pattern making, and casting has been shortened, and the number of patient’s visits can also be reduced. Advances in intraoral scanner technology have increased the precision and accuracy of optical impression, and its indication is progressively widened toward the long span fixed dental prosthesis. This case report describes the long span implant case, and the operator fully utilized digital workflow such as computer-guided implant surgical template and CAD-CAM produced restoration after the digital impression. The provisional restoration and customized abutments were prepared with the optical impression taken on the same day of implant surgery. Moreover, the final prosthesis was fabricated with the digital scan while utilizing the same customized abutment from the provisional restoration. During the data acquisition step, stl data of customized abutments, previously scanned at the time of provisional restoration delivery, were imported and automatically aligned with digital impression data using an ‘A.I. abutment matching algorithm’ the intraoral scanner software. By using this algorithm, it was possible to obtain the subgingival margin without the gingival retraction or abutment removal. Using the digital intraoral scanner’s advanced functions, the operator could shorten the total treatment time. So that both the patient and the clinician could experience convenient and effective treatment, and it was possible to manufacture a prosthesis with predictability.

Evaluation of the accuracy of three different intraoral scanners for endocrown digital impression: An in vitro study / 대한치과보철학회지

Purpose@#The aim of this in vitro study was to evaluate the accuracy of three different intraoral scanners (IOSs) on digital impressions of different types of endocrown cavity preparations. @*Materials and methods@#Two human mandibular molar teeth were prepared with different endocrown abutment designs: one with a buccal wall (Class 2) and the other without a buccal wall (Class 3). Both cavity designs were scanned using a reference desktop scanner (E3) and three different intraoral scanners: Trios3 (TRI group), Cerec Omnicam (CER group), and i500 (I5 group). The obtained Standard Tessellation Language (.stl) datasets were exported to metrology software. The precision was evaluated based on deviations among repeated scan models recorded by each IOS. The trueness was evaluated based on deviations between the reference data and repeated scans. For detecting interaction, data were statistically analyzed using a univariate analysis of variance (ANOVA) and for analyzing the comparison of the test groups data were analyzed by one-way ANOVA and post-hoc Tukey test at the significance level of .05. @*Results@#The deviation values for both cavity designs in the I5 group were significantly lower than those in the other IOS groups in terms of trueness. For both cavity designs, the TRI group exhibited better precision than the other IOS groups. @*Conclusion@#Different technologies of IOS device's and different endocrown prepration designs affected the accuracy of the digital scans.

Dental students’ clinical confidence in denture treatment after clinical experiences / 대한치과보철학회지

Purpose@#The purpose of this study is to investigate dental students’ self-perception of clinical care ability after a denture treatment experience. @*Materials and methods@#Of the 58 fourth-year students at the dental school in 2019, 50 students completed the questionnaire concerning their denture treatment session, including treatment planning and pre-prosthetic treatment (4 questions), clinical and laboratory procedures (20 questions), and students’ opinions on clinical denture education (4 questions). Each question was answered on a five-point scale, of which points four and five, “agree” and “strongly agree” respectively, were classified as positive responses while points one and two, “disagree” and “strongly disagree” respectively, were classified as negative. @*Results@#All the items on clinical and laboratory procedures received a positive response rate of over 60%, and the overall self-perception of the students appeared to be positive. However, the questions on the ability to perform denture treatment independently after graduation received only 48% of positive answer. Those on patient management, explanations of denture precautions, customized tray production, boxing, and work model production were answered with the highest positive response rate whereas those on treatment planning, final impression acquisition, and surveying, were the lowest in each session. @*Conclusion@#The dental students with experience in denture treatment generally have a positive opinion of their clinical care ability, but further education may be necessary to improve their ability to treat their patients independently.

Comparison of Flexural Strength of Three-Dimensional Printed Three-Unit Provisional Fixed Dental Prostheses according to Build Directions

PURPOSE: The aim of this study was to compare the flexural strength of provisional fixed dental prostheses which was three-dimensional (3D) printed by several build directions. MATERIALS AND METHODS: A metal jig with two abutment teeth and pontic space in the middle was fabricated. This jig was scanned with a desktop scanner and provisional restoration was designed on dental computer-aided design program. On the preprocessing software, the build angles of the restorations were arranged at 0°, 30°, 45°, 60°, and 90° and support was added and resultant structure was sliced to a thickness of 100 µm. Processed restorations were printed with digital light processing type 3D printer using poly methyl meta acrylate-based resin. After washing and post-curing, compressive loading was applied at a speed of 1 mm/min on a metal jig fixed to a universal testing machine. The maximum pressure at which fracture occurred was measured. For the statistical analysis, build direction was set as the independent variable and fracture strength as the dependent variable. One-way analysis of variance and Tukey's post hoc analysis was conducted to compare fracture strength among groups (α=0.05). RESULT: The mean flexural strength of provisional restoration 3D printed with the build direction of 0° was 1,053±168 N; it was 1,183±188 N at 30°, 1,178±81 N at 45°, 1,166±133 N at 60°, and 949±170 N at 90°. The group with a build direction of 90° showed significantly lower flexural strength than other groups (P<0.05). The flexural strength was significantly higher when the build direction was 30° than when it was 90° (P<0.01). CONCLUSION: Among the build directions 0°, 30°, 45°, 60°, and 90° set for 3D printing of fixed dental prosthesis, an orientation of 30° is recommended as an effective build direction for 3D printing.

Rehabilitation with implant-supported fixed dental prostheses using digital duplication technique on customized artificial tooth, interim denture and implant surgical template: A case report / 대한치과보철학회지

Bone and soft tissue conditions are important for successful implant treatment. But, the placement itself is also very important. Implants which is installed in the wrong position result in the biological, esthetical and mechanical problems. In order to place an implant in the correct position, the final restoration and diagnostic wax-up should be considered prior to the surgery. If the artificial teeth for the interim denture are directly transferred from the diagnostic wax-up, the operator can try the form of diagnostic wax-up in the mouth. If the surgical template is produced by duplicating the interim denture, the implant can be placed in the planned position. In this case, the polymethyl methacrylate (PMMA) artificial tooth was precisely milled by the digital duplication of diagnostic wax-up. And interim denture was fabricated by using these milled teeth. After the patient adapted for a sufficient period, the implant was placed at the planned position with surgical template produced by duplicating the interim denture. After confirming sufficient osseointegration, the final prostheses were made to reflect the shape of diagnostic wax-up. Through this procedure, the satisfactory functional and esthetic outcome could be acquired.

The use of implant surveyed fixed prosthesis for removable partial denture with a few unilateral remaining teeth: A case report / 대한치과보철학회지

As implant can be covered by National Health Insurance Service (NHIS), it was increased the interest in the removable partial denture (RPD) with the surveyed fixed prosthesis supported by implant fixture. To achieve predictable result, it needs the prudent implant planning by basic principles of RPD and patient's residual ridge. This 67 years old age male had a few unilateral remaining teeth, and hoped the treatment covered by NHIS. As using CAD software, the position of implant is planned with regarding to occlusal table of provisional denture, basic principles of RPD, and resorbed residual ridge. The definitive prostheses can ensure the stability and retention of removable prosthesis. When planning implant fixed prostheses, the digital technique was utilized to consider basic principle of RPD and resorbed residual ridge. As a result, it provided satisfactory prostheses.

Accuracy comparison of buccal bite scans by five intra-oral scanners

PURPOSE: The purpose of this study was to investigate the accuracy of the interocclusal relationship between upper and lower teeth according to the buccal interocclusal record scan using various intraoral scanner systems. MATERIALS AND METHODS: The upper and lower full arch Models with normal occlusion were scanned with 5 intraoral scanners (Cerec Omnicam, CS3500, iTero, Trios, True Definition). Buccal interocclusal record scan was taken only at the left side while occlusion was intentionally raised by 1 mm, 2 mm, 3 mm, and 4 mm with metal cylinder core embedded within polyvinylsiloxane bite registration material at the right molar region. The superimposition analysis was done to evaluate overall three-dimensional deviation and cross-section analysis was done to evaluate the degree and the direction of deviation of interocclusal relationship. RESULTS: From the superimposition study, Cerec Omnicam showed the least deviation (165.5 µm) and CS3500 (369.0 µm) showed the largest (P < 0.01). And the deviation was greater in 3, 4, 2 mm group than 1 mm (P < 0.01). From the cross-section study, Cerec Omnicam showed the farthest deviation (−242.8 µm) and CS3500 showed the closest deviation (312.5 µm) and a significantly high value was shown in 3 mm group. CONCLUSION: Every intraoral scanner has different accuracy in reproducing interocclusal relationship.

Flexural strength of various kinds of the resin bridges fabricated with 3D printing

PURPOSE: Manufacturing with AM (Additive manufacturing) technique has many advantages; but, due to insufficient study in the area, it is not being widely used in the general clinic. In this study, differences of flexural strength among various materials of 3 unit fixed dental prosthesis were analyzed. MATERIALS AND METHODS: A metal jig for specimens that had a 3-unit-fixed dental prosthesis figure were fabricated. The jigs were made appropriately to the specifications of the specimens. Three different kinds of materials of specimens which were NC (mathacrylic esther based), DP-1 (Bisphenol A epoxy acrylate type oligomer based), and DT-1 (urethane acrylate based) were printed with DLP machine. Five specimens for each kind of material were printed with an angle of 30° from the horizontal surface. The specimens were placed on the jig and the flexural strength was measured and recorded using Universal testing machine. The recorded data was analyzed in SPSS using One-way ANOVA and Tukey HSD to determine the significance of the differences of flexural strength among the groups. RESULTS: The flexural strengths of each group were the followings: NC, 1119 ± 305 N; DP-1, 619 ± 150 N; DT-1, 413 ± 65 N. Using One-way ANOVA and Tukey Honestly Significant Difference test, significant difference was found between NC and the other groups (P 0.05). CONCLUSION: Higher flexural strength was shown in 3-unit-fixed dental prosthesis that were 3D printed using a DLP machine with NC material.

Accuracy of several implant bite registration techniques: an in-vitro pilot study

PURPOSE: This study evaluated the accuracies of different bite registration techniques for implant-fixed prostheses using three dimensional file analysis. MATERIALS AND METHODS: Implant fixtures were placed on the mandibular right second premolar, and the first and second molar in a polyurethane model. Aluwax (A), Pattern Resin (P), and Blu-Mousse (B) were used as the bite registration materials on the healing abutments (H) or temporary abutments (T). The groups were classified into HA, HP, HB, TA, TP, and TB according to each combination. The group using the bite impression coping was the BC group; impression taking and bite registration were performed simultaneously. After impression and bite taking, the scan bodies were connected to the lab analogs of the casts. These casts were scanned using a model scanner. The distances between two reference points in three-dimensional files were measured in each group. One-way ANOVA and Duncan's test were used at the 5% significance level. RESULTS: The smallest distance discrepancy was observed in the TB group using the temporary abutments. The Blu-Mousse and HP groups showed the largest distance discrepancy. The TB and BC groups showed a lower distance discrepancy than the HP group (P=.001), and there was no significant difference between the groups using the temporary abutments and healing abutments (P>.05). CONCLUSION: Although this study has limitations as an in-vitro investigation, the groups using the temporary abutments to hold the Blu-Mousse record and bite impression coping showed greater accuracy than the group using the healing abutments to hold the pattern resin record.

RPD framework fabrication using computer-aided design (CAD) and rapid prototyping / 대한치과보철학회지

Nowadays, digital dentistry is generally applied to prosthodontics with fabrication of inlays or any other fixed prostheses by utilizing CAD/CAM (computer-aided design/computer-aided manufacturing) technology and intraoral scanner. However, in fabricating removable prosthesis, there are some limitations for digital technology to substitute conventional casting method. Therefore, approaching removable prostheses fabrication with CAD/CAM technology would be a meaningful trial. In this case report, Kennedy class III mandibular edentulous patient who was in need of increasing the vertical dimension of occlusion was treated with removable partial denture using CAD and rapid prototyping technique. Surveying and designing the metal framework of the partial denture was performed with CAD, and sacrificial plastic pattern was fabricated with rapid prototyping technique. During the follow up period of nine months, the removable partial denture has provided satisfactory results in esthetics and function.

A comparison of the precision of three-dimensional images acquired by 2 digital intraoral scanners: effects of tooth irregularity and scanning direction / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to compare the precision of three-dimensional (3D) images acquired using iTero(R) (Align Technology Inc., San Jose, CA, USA) and Trios(R) (3Shape Dental Systems, Copenhagen, Denmark) digital intraoral scanners, and to evaluate the effects of the severity of tooth irregularities and scanning sequence on precision. METHODS: Dental arch models were fabricated with differing degrees of tooth irregularity and divided into 2 groups based on scanning sequence. To assess their precision, images were superimposed and an optimized superimposition algorithm was employed to measure any 3D deviation. The t-test, paired t-test, and one-way ANOVA were performed (p < 0.05) for statistical analysis. RESULTS: The iTero(R) and Trios(R) systems showed no statistically significant difference in precision among models with differing degrees of tooth irregularity. However, there were statistically significant differences in the precision of the 2 scanners when the starting points of scanning were different. The iTero(R) scanner (mean deviation, 29.84 +/- 12.08 microm) proved to be less precise than the Trios(R) scanner (22.17 +/- 4.47 microm). CONCLUSIONS: The precision of 3D images differed according to the degree of tooth irregularity, scanning sequence, and scanner type. However, from a clinical standpoint, both scanners were highly accurate regardless of the degree of tooth irregularity.

Evaluation of marginal and internal gap under model-free monolithic zirconia restoration fabricated by digital intraoral scanner / 대한치과보철학회지

PURPOSE: The aim of this study was to evaluate the marginal and internal adaptation of monolithic zirconia restoration made without physical model by digital intraoral scanner. MATERIALS AND METHODS: A prospective clinical trial was performed on 11 restorations as a pilot study. The monolithic zirconia restorations were fabricated after digital intraoral impression taking by intraoral scanner (TRIOS, 3shape, Copenhagen, Denmark), computer-aided designing, and milling manufacturing process. Completed zirconia crowns were tried in the patients' mouth and a replica technique was used to acquire the crown-abutment replica. The absolute marginal discrepancy, marginal gap, and internal gap of axial, line angle, and occlusal part were measured after sectioning the replica in the mesiodistal and buccolingual direction. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U test (α=.05). RESULTS: From the adaptation analysis by replica, the statistically significant difference was not found between mesiodistal and buccolingual sections (P>.05), but there was significant difference among the measurement location (P<.01). The amount of absolute marginal discrepancy was larger than those of marginal gap and internal gap (P<.01). CONCLUSION: Within the limitations of this study, the adaptation accuracy of model-free monolithic zirconia restoration fabricated by intraoral scanner exhibited clinically acceptable result. However, the margin of zirconia crown showed tendency of overcontour and cautious clinical application and follow up is necessary.

Clinical evaluation of the removable partial dentures with implant fixed prostheses / 대한치과보철학회지

PURPOSE: The purpose of this study was to identify clinical complications in removable partial denture (RPD) with implant-supported surveyed prostheses, and to analyze the factors associated with the complications such as location of the implant, splinting adjacent prostheses, the type of retentive clasps, Kennedy classification, and opposing dentition. MATERIALS AND METHODS: A retrospective clinical study was carried out for 11 patients (7 male, 4 female), mean age of 67.5, who received RPD with Implant-supported surveyed prostheses between 2000 and 2016. The mechanical complications of 11 RPDs and 37 supporting implant prostheses and the state of natural teeth and peripheral soft tissue were examined. Then the factors associated with the complications were analyzed. RESULTS: The average of 3.4 implant-supported prostheses were used for each RPD. Complications found during the follow-up period of an average of 42.1 months were in order of dislodgement of temporary cement-retained prostheses, opposing tooth fracture/mobility, screw fracture/loosening, clasp loosening, veneer porcelain fracture, marginal bone resorption and mobility of implant, artificial tooth fracture. Complications occurred more frequently in anterior region compared to posterior region, non-splinted prostheses compared to splinted prostheses, surveyed prostheses applied by wrought wire clasp compared to other clasps, and natural dentition compared to other removable prostheses as opposing dentition. There were no significant differences in complications according to the Kennedy classification. CONCLUSION: All implant-assisted RPD functioned successfully throughout the follow-up. However, further clinical studies are necessary because the clinical evidences are still not enough to guarantee the satisfactory prognosis of implant-assisted RPD for long-term result.