The International Journal of Prosthodontics, 04/2020

Purpose: To evaluate the influence of the cervical crown contour on marginal bone loss and soft tissue health around platform-switched, posteriorly placed, two-piece implants. Materials and Methods: A dataset from two previously conducted studies was used. Patients with single two-piece, platform-switched implants in between two natural teeth or adjacent to one natural tooth were included. Clinical parameters and standardized periapical radiographs from 1 month and 5 years after final crown placement were assessed. A new measurement method was developed to analyze geometric values of the cervical crown contour. Interand intraexaminer reliability were assessed. Emergence angles were measured at 1, 2, and 3 mm above the implant shoulder. Linear correlations between variables were determined by calculating Pearson correlation coefficients. Results: A total of 64 patients with 67 posterior implants met the inclusion criteria. At 1, 2, and 3 mm above the implant shoulder, mean emergence angles at the mesial implant sites were 0.5 ± 2.8, 12.8 ± 12.8, and 18.0 ± 11.3 degrees, respectively. At the distal sites, the corresponding values were 2.8 ± 8.3, 16.2 ± 16.6, and 18.7 ± 13.8 degrees, respectively. Mean marginal bone loss between 1 month and the 5-year evaluations was 0.14 ± 0.34 mm at the mesial aspect and 0.26 ± 0.47 at the distal aspect of implants. No correlation with peri-implant bone loss or soft tissue health could be found. No implants showed signs of peri-implantitis. Conclusion: The cervical crown contour at platform-switched, posteriorly placed, two-piece implants showed no correlation with peri-implant marginal bone loss or soft tissue health up to 5 years after implant placement.

Purpose: To test the accuracies of different methods of digital vertical dimension augmentation (VDA) by comparison with a clinical situation. Materials and Methods: Bite registrations with approximately 5 mm of VDA were made in the incisor regions of 10 subjects (mean VDA 4.5 mm). The conventional maxillary and mandibular stone casts in maximum intercuspation (MICP) and VDA bite registrations were digitized for all subjects using a laboratory scanner (control group). Lateral portraits were taken of all subjects to locate the position of the condylar axis. Four different digital VDA methods were compared to the control group: 100% rotation of the mandible referring to the lateral picture (100RL); 85% rotation and 15% translation referring to the lateral picture (85R15TL); 100% rotation in normal mounting mode of the Trios virtual articulator (100R); and jaw-motion analysis (JMA) equipment. The amount of VDA for each experimental group was compared to the control group. The augmented distances between the central incisors and the second molars were measured using 3D analyzing software. The ratio of the augmented distances between the posterior and anterior regions (P/A ratio) was calculated. One-way analysis of variance and multiple comparisons via least significant difference test were carried out to determine statistical significance. Results: The P/A ratio of each group was as follows: Control = 0.61; 100RL = 0.55; 85R15TL = 0.61; 100R = 0.53; JMA = 0.52. Significant differences were observed for control vs JMA and for 85R15TL vs JMA (P < .05). The addition of translational movement was the primary factor for increasing the accuracy of digital VDA, with the lateral picture being a secondary factor. Conclusion: VDA using a virtual articulator with 100% rotation induces an error when compared to the clinical situation. When a clinician performs digital VDA, the setting of 85% rotation and 15% translation produces results closer to the real clinical condition.

Purpose: To investigate differences in the performance of polyether ether ketone (PEEK) frameworks vs traditional metal frameworks for removable partial dentures (RPDs) in terms of OHRQoL, patient preference, periodontal indices, and denture satistfaction. Materials and Methods: Twenty-six participants were recruited to a randomized controlled crossover trial and were provided with either PEEK or cobalt-chromium (Co-Cr) RPDs. After 4 weeks, the participants were provided with the other RPD. After both 4-week testing periods, the participants chose their preferred RPD and were followed up again at 6 months and 1 year. The primary outcome measure was effect on OHIP-20 score, which was compared among patients using repeated measures ANOVA. Secondary outcomes were participant preference compared using chi-square analysis; Plaque Index and Gingival Bleeding Index (PI and GBI, respectively) compared using repeated measures ANOVA; and McGill Denture Satisfaction Questionnaire (MDSQ) score compared between the two 4-week follow-ups using paired-samples t test. Results: Both Co-Cr and PEEK frameworks resulted in a significant improvement in OHIP-20 score (P < .001), but the material was not a significant factor in changes over 1 year (P = .87). There were no statistically significant differences in participant preference at 1 year (P = .491), nor between RPD materials in their effect on GBI (P = .476), PI (P = .967), or MDSQ (P = .368). Conclusion: Both Co-Cr and PEEK RPDs improved OHRQoL to a degree greater than the minimum clinically important difference at 4 weeks, 6 months, and 1 year compared to baseline. No significant preference or improved denture satisfaction score was seen for either material. PEEK frameworks seem to be associated with similar degrees of periodontal effects as Co-Cr frameworks.

Purpose: To evaluate the first-choice treatment options proposed to edentulous patients and the rationale behind them using an internet-based survey conducted among a sample of French dental clinicians. Materials and Methods: From July to December 2018, an internet-based survey was conducted among a sample of 2,000 dental practitioners in order to assess first-choice treatment options proposed to edentulous patients. A total of 349 responses were received, and 310 questionnaires were included for analysis. Results: The majority of clinicians proposed a maxillary complete denture (CD) (59.7%) and mandibular implant overdenture (45.2%) for edentulous patients. Almost 30% of practitioners proposed a CD as the first-choice option for mandibular edentulous patients. Binary logistic regression showed that the likelihood of proposing implant therapy in the maxilla was significantly increased for male practitioners (OR = 2.041, 95% CI = 1.231 to 3.385, P < .05) and for clinicians who had further training in implantology (OR = 2.301, 95% CI = 1.354 to 3.917, P < .05). In the mandible, the likelihood was significantly increased for clinicians who graduated 10 to 19 years ago (OR = 5.312, 95% CI = 1.331 to 21.208, P < .05), had further training in implantology (OR = 2.246, 95% CI = 1.121 to 4.500, P < .05), had expectations of comfort and stability (OR = 11.810, 95% CI =5.289 to 26.372, P < .001), and proposed the treatment according to national and international recommendations (OR = 3.252, 95% CI = 1.208 to 8.755, P < .05). Conclusion: The research results suggest that proposing either a CD or implant restorations for treatment of edentulous patients depends on training and specific skills in implantology.

Purpose: To investigate the reverse torque values of abutment screws subjected to various surface modifications. Materials and Methods: Sixty abutment screws were divided into two groups of 30 each: with thermomechanical cycling (240,000 cycles) and without thermomechanical cycling. Each group was then divided into three subgroups according to surface treatment: nontreated (NT, n = 10); anodic oxidation (AO, n = 10); and diamond-like carbon (DLC) coating (DLC, n = 10). All abutment screws were tightened to 30 Ncm using a digital torque meter. The reverse torque values of the abutment screws with and without thermomechanical cycling were then measured. The percentage of deviation (PERDEV) for reverse torque values was calculated. Two-way analysis of variance followed by Tukey Honest Significant Difference test were used for intergroup comparisons. Results: Significant differences were found among the PERDEV values of the groups based on thermomechanical cycling and surface treatment (P < .001 for each). A significant interaction was found between surface treatment and thermomechanical cycling (P < .001). Conclusion: Reverse torque values of abutment screws were found to be higher after surface treatments. The abutment screws with AO exhibited the lowest torque value loss in groups with and without thermomechanical cycling.

Purpose: To evaluate the dimensional accuracy of impressions made using a new fast-setting polyether material. Materials and Methods: A metallic reference model with two crown preparations, one inlay preparation, and three stainless steel precision balls was digitized to create a digital reference model. Sixteen one-step impressions were made for each of the four study groups, differing in impression material (regularsetting polyether [RSP] vs fast-setting polyether [FSP]) and technique (monophase vs dualphase), for a total of 64 specimens. Plaster casts fabricated from these impressions were digitized using 3D scans. Global accuracy was studied by evaluating distance and angle deviations between the replica and the reference model. Local accuracy was described in terms of trueness and precision of the aligned individual abutment tooth surfaces. Results: For all impression materials and techniques, the local accuracy at the abutment tooth level was excellent. For surfaces prepared for crowns, mean trueness was < 10 μm, and mean precision < 12 μm. Inlay surfaces were associated with higher inaccuracies (mean trueness < 21 μm and mean precision < 37 μm). The greatest global inaccuracies were generally measured for the cross-arch span, with mean distance changes between –55 μm and –94 μm. For all aspects of studied accuracy, impressions with FSP were at least comparable to those fabricated with RSP. Conclusion: Within the limitations of this study, all tested polyether materials would allow for clinically acceptable impression making. The new fast-setting material could be an alternative to regular-setting polyether materials, especially for single crowns and small fixed partial dentures.

Purpose: To compare the influence of surface roughness and accelerated aging on the mechanical properties of polymer-based and ceramic CAD/CAM materials. Materials and Methods: Three polymers (Lava Ultimate [LVU], VITA ENAMIC [ENA], and Shofu Block HC [SFB]) and one ceramic (IPS Empress CAD [EMP]) were selected for this study. The specimens were treated with the aim of measuring surface roughness (Ra [mm]) and its influence on the mechanical properties. The treatments were: polishing (POL); etching with 9.6% hydrofluoric acid for 90 seconds (ETC); airborne-particle abrasion with 50-μm aluminum oxide at 2-bar pressure (SBT); and airborne-particle abrasion with 50-μm aluminum oxide at 2-bar pressure plus etching with 9.6% hydrofluoric acid (SAC) for 90 seconds. Before and after the accelerated aging (AA) protocol (30,000 cycles, 5°C and 55°C), the specimens were subjected to the 3-point bending test. The data were analyzed with two-way and three-way ANOVA and post hoc Tukey test (P < .05). Results: The surface roughness ranged from 0.24 μm to 1.96 μm, with statistically significant differences (P < .05). The highest surface roughness, in descending order, was exhibited by: LVU > SFB > EMP > ENA. The AA demonstrated an influence on the flexural strength of LVU, ENA, and SFB. The surface treatment did not affect the flexural moduli of the materials tested. The LVU and SFB showed decreased moduli of resilience after the AA; however, modulus of resilience was not influenced by surface treatment. Conclusion: The polymer-based materials were affected by AA. In addition, surface treatment could jeopardize their mechanical properties in certain conditions.

Purpose: To systematically review the current evidence on clinical and patient-reported outcomes of implantsupported palatal obturator prostheses. Materials and Methods: An electronic search of the PubMed, Web of Science, and Cochrane databases was carried out in June 2019. The titles and abstracts of all articles were screened by two independent reviewers. The references of the subsequently selected studies were further screened for potential articles. Assessment of the selected full texts was performed independently according to established inclusion and exclusion criteria. The quality of the selected studies was determined using the Newcastle-Ottawa scale. Interrater agreement on study selection was calculated using Cohen kappa statistic. Results: The search yielded a total of 2,797 records. Ten studies were selected for data extraction, with a Cohen kappa value of 0.856. Five studies were prospective, and five were retrospective. The survival rates for conventional implants ranged from 21.42% to 100%, whereas for zygomatic implants, the survival rates varied from 30% to 100%. Four studies reported prosthodontic complications, with screw loosening being the most common. Patient quality of life (QoL) was analyzed in six studies. Conclusion: In spite of the limitations of the present review, it can be concluded that the clinical outcomes are acceptable in terms of survival rates, implant and prosthodontic complications, and QoL associated with implant-supported maxillary obturator prostheses. QoL of implant-supported prostheses in these patients are acceptable. The general study design was not homogenous between studies.

Purpose: To research and develop a novel virtual articulator system (the PN-300) based on computer binocular vision, raster scanning, and simulation technology and to conduct a preliminary evaluation of its accuracy. Materials and Methods: Two digital cameras were used to build the trajectory-tracking part of the virtual articulator system, and cameras combined with a projection module were used to form the scanning part of the system. The most prominent feature of the PN-300 is its ability to simultaneously obtain the 3D data of the subject's teeth and the movement trajectory of the mandible relative to the maxilla. The PN-300 recorded the linear, circular, and rectangular quadrilateral movements of a high-accuracy 3D electronic translation stage. The accuracy of measurement of the inclination of incisal guidance derived from the PN-300 based on the PROTAR evo7 articulator was also estimated. Results: The measurement error was below 100 μm for the linear and circular movements, and the angle error was within 0.2 degrees for the rectangular quadrilateral movements. The error of inclination of protrusive incisal guidance was 1.51 ± 0.68 degrees, and for incisal guidance was 0.82 ± 0.55 degrees. Trajectories and incisal 3D data obtained by the PN-300 were combined with data from plaster models and CBCT to simulate mandibular movement and to calculate the trajectories of the condyle. Conclusion: The PN-300 achieved a good accuracy for recording mandibular movement and can be expected to calculate the movement of the condyle.

Purpose: To assess the feasibility of using an intraoral scanner for data acquisition of maxillectomy defects. Materials and Methods: In 10 patients who had undergone a maxillectomy, the maxillectomy defects in dentate and edentulous maxillary arches were intraorally scanned. Intraoral photographs were also taken using a digital camera for comparison. Results: Adequate scanning was achieved for the nondefect side of the maxilla and for residual teeth. In some cases, it was impossible to scan the maxillectomy defect, especially the deep sites. Conclusion: Improved intraoral scanning technology will increase the feasibility of its use in maxillofacial prosthetics.

Cusp fractures occur frequently in endodontically treated teeth with large restorations and no cusp protection. These fractures often lead to challenging clinical decisions, such as whether to undertake complex restorative management or extraction of the affected teeth. This article reports the surgical and restorative management of two teeth with fractures exceeding the biologic width to juxtacrestal and subcrestal levels, respectively, and describes a new technique for such treatment.