Comparison of clinical outcomes between single metal-ceramic and zirconia crowns.

STATEMENT OF PROBLEM: Evidence comparing the survival of zirconia crowns with metal-ceramic crowns is sparse. Knowledge of their survival and a comparison of their clinical outcomes would improve clinical decision making. PURPOSE: The purpose of this university-based study was to compare the survival, failures, biological and technical complications encountered with zirconia and metal-ceramic crowns restored and followed up over a similar period. MATERIAL AND METHODS: This retrospective chart review consisted of 403 patients treated at the University of Toronto, Faculty of Dentistry, predoctoral dental clinic in whom zirconia (n=209) and metal-ceramic (n=306) crowns were inserted between September 2015 and July 2016 and followed for up to 7 years. Outcome measures included failure, causes for failure, and complications associated with survival. Inferential statistical analysis included the chi-squared test, t test, Mann-Whitney test, Bonferroni-adjusted z-test, Kaplan-Meier survival test, and logistic regression to examine differences between crown types and explore crown failures (α=.05). RESULTS: The mean follow-up period was 3.00 years (median 2.58 years). Forty-one (8.0%) crowns had no follow-up, with no difference in follow-up between crown type: metal-ceramic n=23(7.5%), zirconia n=18(8.6%), χ²(1)=0.20, P=.652). Excluding those with no follow-up, the follow-up time between metal-ceramic (mean=3.07, median=2.58) and zirconia (mean=3.54, median=3.32) crowns was statistically similar (P=.052). There were 62 anterior crowns (12.0%) and 453 posterior crowns (88.0%), χ²(1)=22.40, P<.001, with no difference between groups. Overall, 44 crowns (8.5%) failed, 30 (9.8%) metal-ceramic and 14 (6.7%) zirconia, with no statistical difference in proportion of failed crowns between groups (χ²(1)=1.53, P=.216). There were 35 crowns with biological failures (6.8%), 26 (8.5%) in the metal-ceramic and 9 (4.4%) in the zirconia group, with no statistical difference between groups (χ²(1)=3.33, P=.068). Nine crowns had technical failures (1.7%), 4 (1.4%) in the metal-ceramic group and 5 (2.5%) in the zirconia group, with no statistical difference between groups (χ²(1)=0.73, P=.394). Biological (79.5%) rather than technical complications were found to be the most frequent cause of failure, goodness-of-fit χ²(1)=15.36, P<.001. Tooth fracture (50.0%) specifically was found to be the most frequent cause of failure, χ²(3)=21.27, P<.001. The total number of crowns that survived was 471 (91.5%); 276 (90.1%) were metal-ceramic and 195(93.3%) zirconia. The survival time (years) for metal-ceramic was mean=6.26, 95% CI [6.01-6.51] and for zirconia crowns mean=6.54, 95% CI [6.31-6.77]. Of the crowns that survived, 370 (78.6%) had no clinical complications, and 101 (21.4%) crowns demonstrated similar clinical complications, with no statistical differences between groups. CONCLUSIONS: Within the study follow-up time, the survival of monolithic zirconia and metal-ceramic crowns was 91.5%, with similar clinical complications between groups. Biological complications, especially tooth fracture, were a significantly more frequent complication with both types of crowns.

Effect of artificial aging on optical properties and crystalline structure of high-translucency zirconia.

PURPOSE: To investigate the effect of different in vitro aging protocols on the optical properties and crystalline structure of high-translucency (HT) zirconia. MATERIALS AND METHODS: Thirty-six specimens of HT and extra-high translucency (XT) zirconia were divided into three groups: control (CO)-no treatment; hydrothermal aging (HA)-autoclave aging for 12.5 h at 134°C, 2 bar; clinically related aging (CRA)-aging in the chewing simulator for 1.2 million cycles, followed by 50,000 thermocycles (5-55°C) and immersion in HCl (pH 1.2) for 15 h. Optical properties, crystalline structure, and surface roughness were analyzed and compared using analysis of variance (5% significance level). RESULTS: There was no statistically significant effect of aging on translucency (p = 0.10), but CRA promoted the development of a high contrast ratio (p = 0.03). Aging did not cause significant color changes for HT (p = 0.65) or XT (p = 0.36). The proportion of monoclinic crystals increased to 40% for HT-zirconia after HA and 5% after CRA. No monoclinic crystals were detected for XT groups. There was no effect of aging on surface roughness (p = 0.77). CONCLUSIONS: Although hydrothermal aging has been widely used to verify zirconia crystalline stability, it did not generate an effect similar to clinically related aging on the optical properties and crystalline structure of zirconia. HA affected the crystalline structure of HT-zirconia, and CRA compromised the optical properties of XT zirconia.

Postinsertion adjustment appointments and their association with cast removable partial denture survival.

STATEMENT OF PROBLEM: Successful outcomes with cast removable partial dentures (RPDs) are dependent on adequate fabrication and adjustments at the delivery appointment. Evaluation of the number and frequency of postinsertion follow-up appointments helps determine whether the prosthesis continues to fit comfortably and whether function and esthetics continue to be satisfactory. Reports on the number of appointments and frequency and type of adjustments required for RPDs following insertion are sparse. PURPOSE: The purpose of this university-based population study was to determine the number of appointments and type of adjustments following RPD insertion and their association with patient demographics, type of RPD, and denture survival. MATERIAL AND METHODS: This retrospective clinical study examined the records of 257 patients at the University of Toronto, Faculty Dentistry, wearing 308 RPDs inserted between 2013 and 2014 with a 5-year follow-up. The outcome measures investigated included postinsertion appointments, type of adjustments, and denture survival. RESULTS: A total of 48.1% of the dentures (19.5% tissue supported; and 28.6% tooth supported) were maxillary, and 51.9% (34.7% tissue supported; and 17.2% tooth supported) mandibular. Most patients (68.9%) had 1 to 3 postinsertion appointments, with 78.6% having no major adjustments. Twenty-six dentures failed (failure rate 8.4%), with the failure-free time estimated at 4.58 years (95% confidence interval (CI) 4.42-4.73 years, Kaplan-Meier survival analysis). Failed dentures were significantly associated with more minor adjustments (Mean (M)=4.12, SD=3.90, Kruskal-Wallis (K-W) P=.027; OR=1.18; 95% CI 1.05-1.32, P=.006). More minor adjustments were needed for mandibular dentures (multivariable Poisson regression (MPR) P=.003) compared with maxillary dentures. More major adjustments were needed for maxillary dentures (MPR P=.030) compared with mandibular dentures. More minor and major adjustments were needed for dentures that were remade from within 5 years to beyond 10 years compared with first time denture wearers (MPR P<.001). Patients with musculoskeletal disorders required a significantly higher number of minor adjustments (M=3.67, MPR P<.001) and appointments (M=3.87, MPR P<.001) than those without these disorders. CONCLUSIONS: The 5-year survival of RPDs following insertion was estimated at 91.6%. Most patients required 1 to 3 appointments after insertion. Mandibular RPDs required significantly more minor adjustments, and maxillary RPDs more major adjustments. More minor and major adjustments were needed for dentures that were remade at any time previously compared with first time denture wearers.

Impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency.

BACKGROUND: Whether precise orthodontic detailing of occlusion impacts masticatory function is unknown. In this study, we aimed to assess the impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency. MATERIALS AND METHODS: Fifty-four adults who completed orthodontic treatment were categorized into two groups using the American Board of Orthodontics (ABO) model grading system: one meeting ABO standards (ABO, N = 29), the other failing to meet them (non-ABO, N = 25). The electromyographic (EMG) signals of the anterior temporalis (AT) and superficial masseter muscles were recorded bilaterally during static (clenching) and dynamic (gum chewing) tests. Chewing efficiency was measured by calculating the median particle size (MPS) and broadness of particle distribution (BPD) after five chewing trials of experimental silicone food at a standardized chewing rate. RESULTS: Participants of the ABO group had a slightly more symmetric activation of the AT muscles during clenching (P = 0.016) and chewed a gum at a slower rate (P = 0.030). During the standardized chewing test with silicone food, ABO subjects had slightly greater EMG potentials at all muscle locations than non-ABO individuals (all P < 0.05). MPS and BDP did not differ significantly between groups (all P > 0.05). LIMITATIONS: The severity of the initial malocclusion of the study participants was not in the statistical model as a potential confounder on the outcome measures. CONCLUSIONS: Meeting ABO standards contributes to a slightly more balanced activation of the temporalis muscles during clenching and more efficient muscle recruitment during chewing but does not improve chewing efficiency.

Biofilm on the tracheoesophageal voice prosthesis: considerations for oral decontamination.

The tracheoesophageal puncture (TEP) restores verbal communication after total laryngectomy using a one-way valved voice prosthesis (VP). Microbial colonization can shorten VP device life. Our aims were to investigate patterns of prosthetic and oral colonization, and record changes in VP device life after targeted decontamination. We conducted a retrospective review of TEP clinic patients who underwent microbial analysis of the VP between 01/2003 and 07/2013. Two subgroups were analyzed: (1) patients with microbial analysis of the VP and the mouth were analyzed to identify patterns of common contamination, and (2) patients who were prescribed targeted oral decontamination on the basis of the microbial analysis of the VP were analyzed to evaluate effects on device life. Among 42 patients, 3 patients had only fungal, 5 only bacterial, and 33 had polyspecies fungal and bacterial colonization. In the TEP-oral microflora subgroup (n = 15), 7 had common microorganisms in the mouth and on the VP. Among the decontamination subgroup (n = 23), 6 patients received broad spectrum rinse, 16 antifungal agents and 13 antibiotics, or a combination thereof. After targeted decontamination, the median device life of prostheses improved from 7.89 to 10.82 weeks (p = 0.260). The majority of patients with a suboptimal VP device life in this pilot had polyspecies bacterial and fungal colonization. VPs rarely had fungal contamination alone (3 %), and non-albicans fungal species were more common than expected. For these reasons, we are exploring the use of targeted decontamination regimens that were associated with 1.4-fold improvement in VP duration.

Accuracy of a novel prototype dynamic computer-assisted surgery system.

OBJECTIVES: To implement and evaluate the accuracy of a prototype dynamic computer-assisted surgery (CAS) system for implant osteotomy preparation and compare its accuracy vs. three commercial static CAS systems and the use of an acrylic stent. MATERIAL AND METHODS: Eight osteotomies were prepared in radiopaque partially edentulous mandible and maxilla typodonts. After cone-beam CT acquisition, DICOM files were imported into a prototype dynamic, and three static CAS systems (NobelClinician, Simplant, and CoDiagnostiX). Implant placements were planned to replicate the existing osteotomies and respective guides were requisitioned, along with one laboratory-made acrylic guide. The eight osteotomies per jaw were transferred to one typodont pair mounted in a manikin in a clinical setting and the process was repeated for four additional pairs. The 80 (two jaws × eight holes × five pairs) osteotomies were filled with radiopaque cement in-between the testing series. Three clinicians experienced with the use of the static CAS softwares used in this study prepared each 400 (80 holes × five modalities) osteotomies. One clinician repeated the experiment twice, resulting in a total of 2000 (five clinicians × 400) osteotomies. The lateral, vertical, total, and angular deviations of the actual vs. the original osteotomies in the master typodonts were measured using stereo optical tracking cameras. Linear regression statistics using generalized estimating equations were used for comparisons between the five modalities and omnibus chi-square tests applied to assess statistical significance of differences. RESULTS: The prototype dynamic CAS system was as accurate as other implant surgery planning and transfer modalities. The dynamic and static CAS systems provide superior accuracy vs. a laboratory-made acrylic guide, except vertically. Both dynamic and static CAS systems show on average <2 mm and 5 degrees error. Large deviations between planned and actual osteotomies were occasionally observed, which needs to be considered in clinical practice. CONCLUSIONS: The prototype dynamic CAS system was comparably accurate to static CAS systems.

Comparative temporospatial expression profiling of murine amelotin protein during amelogenesis.

Tooth enamel is formed in a typical biomineralization process under the guidance of specific organic components. Amelotin (AMTN) is a recently identified, secreted protein that is transcribed predominantly during the maturation stage of enamel formation, but its protein expression profile throughout amelogenesis has not been described in detail. The main objective of this study was to define the spatiotemporal expression profile of AMTN during tooth development in comparison with other known enamel proteins. A peptide antibody against AMTN was raised in rabbits, affinity purified and used for immunohistochemical analyses on sagittal and transverse paraffin sections of decalcified mouse hemimandibles. The localization of AMTN was compared to that of known enamel proteins amelogenin, ameloblastin, enamelin, odontogenic ameloblast-associated/amyloid in Pindborg tumors and kallikrein 4. Three-dimensional images of AMTN localization in molars at selected ages were reconstructed from serial stained sections, and transmission electron microscopy was used for ultrastructural localization of AMTN. AMTN was detected in ameloblasts of molars in a transient fashion, declining at the time of tooth eruption. Prominent expression in maturation stage ameloblasts of the continuously erupting incisor persisted into adulthood. In contrast, amelogenin, ameloblastin and enamelin were predominantly found during the early secretory stage, while odontogenic ameloblast-associated/amyloid in Pindborg tumors and kallikrein 4 expression in maturation stage ameloblasts paralleled that of AMTN. Secreted AMTN was detected at the interface between ameloblasts and the mineralized enamel. Recombinant AMTN protein did not mediate cell attachment in vitro. These results suggest a primary role for AMTN in the late stages of enamel mineralization.

The effect of accelerated aging on crystalline structures and optical properties of different monolithic zirconia: A qualitative systematic review.

OBJECTIVE: This study aimed to systematically review the literature related to the impact of low temperature degradation (LTD) on the crystalline structures and optical properties of different types of dental monolithic zirconia materials. METHODS: The systemic review was performed based on the PRISMA statement. In vitro studies investigating the effect of accelerated aging in autoclave (2 bar pressure 134°C - ISO standard 13356-2008) on the crystalline structure and/or optical properties of Yttria-partially stabilized zirconia (Y-PSZ) were included. Specific search terms were used for peer-reviewed articles published in PubMed, Ovid MEDLINE, and EMBASE databases. RESULTS: From 286 eligible articles, 51 articles were selected for full-text analysis, 10 failed to meet the inclusion criteria, and 41 articles were included in this review. Autoclave aging (30 min - 300 h) results in an increase in monoclinic phase (m) content up to 80% for tetragonal zirconia and reaching saturation after 35 h of autoclave aging. All included articles reported less than 1% of monoclinic phase for cubic zirconia after autoclave aging. Translucency parameter was reported between 2.34 and 19.7 after autoclave aging (4-100 h). For same aging time, contrast ratio ranged between 0.48 and 0.95. SIGNIFICANCE: An increase in monoclinic phase was reported for tetragonal zirconia, while cubic zirconia demonstrates resistance to LTD. The optical properties for all zirconia materials investigated seem more compromised with increasing aging time.

Room-temperature atomic layer deposition of SiO2 on microcracked ZrO2 layers.

Yttria-stabilized zirconia (Y-SZ) has become a reliable material option to restore severely compromised teeth. Y-SZ materials are prone to low-temperature degradation (LTD), which generates a tetragonal-to-monoclinic (t-m) transformed, porous layer. We suggest that room-temperature atomic layer deposition (RT-ALD) could be used for the infiltration and deposition of nanoscale SiO2 film over this layer, creating a protective hybrid surface against further degradation by LTD. This study investigated the potential of developing a Y-SZ transformed layer under controlled conditions for the infiltration of silica using RT-ALD, aiming to develop a hybrid zirconia-silica interface, and to investigate the effect of silica deposition/infiltration via RT-ALD on the surface roughness and wettability of zirconia-based materials. Sintered specimens (14 mm × 4 mm x 2 mm) were prepared from four different Y-SZ materials (n = 40): low translucency 3 mol % Y-SZ (3Y-LT; Ceramill ZI, Amann Girrbach); high translucency 4 mol % Y-SZ (4Y-HT; Ceramill Zolid); and two high translucency 5 mol % Y-SZ (5Y-HT - Lava Esthetic, 3M; 5Y-SHT - Ceramill Zolid, FX white). Specimens were exposed to hydrothermal treatment (HTT) to develop similar depths of crystalline changes. RT-ALD was used to deposit a thin film of silica (SiO2). Surface roughness and wettability analyses were performed to investigate the effect of treatment (HTT and RT-ALD) and material on Y-SZ surface properties, and data was analyzed by two-way ANOVA and Tukey HSD (p < 0.05). RT-ALD and HTT-RT-ALD treated specimens of 3Y-LT and 5Y-HT materials were exposed to further hydrothermal aging (HA) and the surface was characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS). There was a significant interaction effect of material and treatment (HTT and RT-ALD) on roughness (p = 0.02), and surface wettability (p < 0.001). Silica deposition via RT-ALD resulted in a significant increase in surface roughness of all materials tested, while surface wettability was either improved or not changed based on the material type and HTT exposure. Nanofilms of SiO2 were successfully deposited on Y-SZ materials and infiltrated 3Y-LT zirconia.

Improving effectiveness of dental students' feedback and course evaluation.

Dental students providing feedback about a course they take, in a timely manner, benefits not only teachers, but also indirectly the students themselves, especially if given with confidence in a constructive manner. Therefore, the aim of this study was to train students on how to give feedback, to ask them to provide feedback before and after the instructions were given, and analyze the change in their responses. Participants were students who attended the second-year preclinical course in prosthodontics. They were asked to provide feedback anonymously with online surveys after completing modules of the course during the academic year. There was no intervention prior to the first feedback; however, before providing the second feedback, students were asked to read a 1-page handout related to feedback modalities. Following this, an interactive workshop in feedback was provided prior to the third survey. The received responses were ranked as either: neutral, positive, negative, or constructive and were analyzed using a mixed repeated measures test with Bonferroni correction at a 0.05 significance level. The results showed a higher number of constructive and positive responses than both neutral and negative feedback (P ≤ 0.05) within the same surveys, but no interaction effect was found between the surveys (P = 0.076). Our data showed an increase in constructive feedback provided by students after the 2 different training methods, but the modality of delivery did not seem to significantly influence the results. In summary, training students on how to provide constructive feedback may be beneficial for teachers to improve their courses.

Investigational Clinical Trial of a Prototype Optoelectronic Computer-Aided Navigation Device for Dental Implant Surgery.

PURPOSE: New digital technologies enable real-time computer-aided (CA) three-dimensional (3D) guidance during dental implant surgery. The aim of this investigational clinical trial was to demonstrate the safety and effectiveness of a prototype optoelectronic CA-navigation device in comparison with the conventional approach for planning and effecting dental implant surgery. MATERIALS AND METHODS: Study participants with up to four missing teeth were recruited from the pool of patients referred to the University of Toronto Graduate Prosthodontics clinic. The first 10 participants were allocated to either a conventional or a prototype device study arm in a randomized trial. The next 10 participants received implants using the prototype device. All study participants were restored with fixed dental prostheses after 3 (mandible) or 6 (maxilla) months healing, and monitored over 12 months. The primary outcome was the incidence of any surgical, biologic, or prosthetic adverse events or device-related complications. Secondary outcomes were the incidence of positioning of implants not considered suitable for straightforward prosthetic restoration (yes/no); the perception of the ease of use of the prototype device by the two oral surgeons, recorded by use of a Likert-type questionnaire; and the clinical performance of the implant and superstructure after 1 year in function. Positioning of the implants was appraised on periapical radiographs and clinical photographs by four independent blinded examiners. Peri-implant bone loss was measured on periapical radiographs by a blinded examiner. RESULTS: No adverse events occurred related to placing any implants. Four device-related complications led to a switch from using the prototype device to the conventional method. All implants placed by use of the prototype device were in a position considered suitable for straightforward prosthetic restoration (n = 21). The qualitative evaluation by the surgeons was generally positive, although ergonomic challenges were identified. All study participants were present for the 1-year examination (n = 20 patients, 41 implants, 32 superstructures), and no complications or failures with any implants or superstructures were revealed. The peri-implant bone loss was less than 1 mm for all implants. CONCLUSION: Within the limitations of this trial, the prototype device provided placement of dental implants without adverse events.

Benchmarking Outcomes in Implant Prosthodontics: Partial Fixed Dental Prostheses and Crowns Supported by Implants with a Turned Surface over 10 to 28 Years at the University of Toronto.

PURPOSE: The aim of this noninterventional, retrospective study was to benchmark the outcomes of patients with partial fixed prostheses supported by implants treated at the University of Toronto at least 10 years earlier. A study protocol for assessing outcomes on like patients developed at the University of Bern, Switzerland, was followed. MATERIALS AND METHODS: All patients who had received at least one implant before 2002 were considered eligible to be included in the study (n = 298). The treatment histories were recorded from the patient chart of the participants, or from the participants' dentists by consent. Calibrated clinicians examined the study participants clinically and radiologically and recorded peri-implant mucosal status and observable technical and mechanical failures. Past adverse events were identified in the patient charts. Independent assessors measured bone levels on digitized radiographs. Statistical analysis included descriptive statistics at implants, teeth, and study participant levels, respectively. RESULTS: Of the 298 eligible patients, 121 attended a clinical examination (41%), while 12 declined (4%). The 121 study participants had received 321 implants between 1983 and 2001. The implants showed a success rate of 88.9% and a survival rate of 94% after an average of 17.5 years (SD 5.2, range 10 to 28 years). Approximately 5% of the surviving implants showed signs, or were associated with a prior history, of peri-implantitis. The distance from the implant shoulder to the first bone contact varied from -3 mm to 7 mm (mean = 1.52 mm [SD 1.57], median = 2.2 mm). Approximately half of the study participants had experienced at least one defect of their superstructure, representing a 52% "success rate," while the survival rate was 70%. The majority were very satisfied or satisfied with the treatment (102/121). CONCLUSION: A high proportion (94%) of conventional machined Brånemark System implants placed between 1983 and 2001 remained in function after an average of 17.5 years. The original superstructures predominantly fabricated as prefabricated acrylic teeth and acrylic resin reinforced with a cast palladium-silver alloy core were still in place for 70% of the participants, and 48% of the superstructures had never undergone any form of repairs.

Targeted overexpression of amelotin disrupts the microstructure of dental enamel.

We have previously identified amelotin (AMTN) as a novel protein expressed predominantly during the late stages of dental enamel formation, but its role during amelogenesis remains to be determined. In this study we generated transgenic mice that produce AMTN under the amelogenin (Amel) gene promoter to study the effect of AMTN overexpression on enamel formation in vivo. The specific overexpression of AMTN in secretory stage ameloblasts was confirmed by Western blot and immunohistochemistry. The gross histological appearance of ameloblasts or supporting cellular structures as well as the expression of the enamel proteins amelogenin (AMEL) and ameloblastin (AMBN) was not altered by AMTN overexpression, suggesting that protein production, processing and secretion occurred normally in transgenic mice. The expression of Odontogenic, Ameloblast-Associated (ODAM) was slightly increased in secretory stage ameloblasts of transgenic animals. The enamel in AMTN-overexpressing mice was much thinner and displayed a highly irregular surface structure compared to wild type littermates. Teeth of transgenic animals underwent rapid attrition due to the brittleness of the enamel layer. The microstructure of enamel, normally a highly ordered arrangement of hydroxyapatite crystals, was completely disorganized. Tomes' process, the hallmark of secretory stage ameloblasts, did not form in transgenic mice. Collectively our data demonstrate that the overexpression of amelotin has a profound effect on enamel structure by disrupting the formation of Tomes' process and the orderly growth of enamel prisms.