The International Journal of Prosthodontics, 05/2021

Purpose: To investigate the relationships among occlusion time (OT), disocclusion time (DT), occlusal load distributions, and simultaneous electromyographic (EMG) recordings of the anterior temporalis (AT) and masseter (MM) muscles during centric and lateral movements in patients with unilateral temporomandibular disorder (TMD) pain and in asymptomatic control subjects. Materials and Methods: Twelve healthy and 13 unilateral TMD subjects participated in the present study. The diagnosis of unilateral TMD was verified with joint vibration analysis (JVA) of the temporomandibular joints (TMJs) using BioJVA software. Simultaneous computerized digital occlusal analysis using T-Scan III (Tekscan) and recording of the EMG activity of the MM and TA using BioEMG III (BioResearch Associates) were performed in the intercuspal position and during right and left lateral movements. In intercuspation and lateral movement records, EMG activity of the masticatory muscles, OT, DT, and bite-force distribution ratios were evaluated. Results: No statistically significant differences were observed in OT, DT, or EMG activity of the MM and TA muscles between controls and patients with unilateral TMD in the intercuspal position. In unilateral TMD patients, DT of the painful side was significantly higher than in the control group and compared to the nonpainful side (P < .05). For lateral movements, bite-force distribution on the nonworking side in TMD patients showed statistically significantly higher values than in control subjects. In controls, the EMG activity of the working-side AT was higher than on the nonworking side and compared to the nonpainful side in TMD patients (P < .05). However, EMG activity of the MM and AT muscles did not show a difference between the working side and nonworking side in the painful side of TMD patients. Conclusion: In the intercuspal position, there was no difference in OT, distribution of force, or EMG activity of the masticatory muscles observed between the control group and unilateral TMD pain patients. However, in lateral movements, the painful side of the unilateral TMD patients revealed increased nonworking-side AT activity and distribution of force with higher DT.

Purpose: To assess the clinical, technical, and esthetic outcomes of directly veneered zirconia abutments cemented onto nonoriginal titanium bases over a 3-year follow-up. Materials and Methods: A total of 24 healthy patients with a single missing tooth in the maxilla or mandible (incisors, canines, or premolars) received a two-piece implant with a screw-retained veneered zirconia restoration extraorally cemented onto a titanium base abutment. Baseline measurements and follow-up examinations were performed at 6 months, 1 year, and 3 years following loading. Radiographic, clinical, technical, and esthetic parameters were assessed. Wilcoxon signed rank test was used to analyze the data. Results: Mean marginal bone levels measured 0.54 ± 0.39 mm (median: 0.47 mm, range: 0.07 to 1.75 mm) at baseline and 0.52 ± 0.39 mm (median: 0.39 mm, range: 0.06 to 1.33 mm) at 3 years. Mean probing depth around the implants increased from 3.0 ± 0.6 mm at baseline to 3.8 ± 0.8 mm at 3 years (P = .001). Bleeding on probing changed from 27.1% ± 20.7% at baseline to 51.5% ± 26.1% at 3 years (P = .001). The mean plaque control record amounted to 11.1% ± 21.2% at baseline and 14.4% ± 13.89% at 3 years (P = .261). Two implants were lost at 3.5 and 30 months postloading due to periimplantitis, resulting in a 91.7% implant survival rate. Patient satisfaction was high at 3 years. Conclusion: Zirconia restorations cemented onto the tested nonoriginal titanium bases should not be recommended for daily clinical use, as they were associated with significant increases in BOP and PD values and varying marginal bone levels 3 years after placement.

Purpose: To evaluate the incidence of ultrathin ceramic veneer fractures with different preparation protocols over a period of 36 months and the possible relationship with local- and patient-related factors. Materials and Methods: Adult patients who received ceramic veneers for improvement in smile esthetics were selected from a private practice pool. Restorations were grouped as conventional (prep) or ultrathin ceramic veneers following either a minimal preparation (min-prep) or no tooth preparation (no-prep) protocol. After veneer bonding, all patients were followed up at intervals of 6 months up to 36 months. A panel of clinical outcomes was recorded, and patient satisfaction was assessed at 36 months. Results: The study sample was formed by 49 patients who received a total of 194 veneers. Twelve veneers were prep, 125 were min-prep, and 57 were no-prep. Total fracture occurrence was 9.8% in 13 participants. No fractures were observed in prep veneers, while 16 out of 125 min-prep and 3 out of 57 no-prep veneers had fractures. Most fractures (13 out of 19) occurred early, within the first 12 months after bonding. Out of 194 veneers, only 1 had a catastrophic failure (0.5%), 3 had large (≥ 1 mm) chippings (1.5%), and 15 had minor (< 1 mm) chippings (7.7%). A generalized estimating equation model revealed that the odds of veneer fracture were significantly higher in men (odds ratio [OR] = 11.29), in patients who exhibited tooth wear at baseline (OR = 5.54), and in central (OR = 13.56) and lateral (OR = 10.43) incisors compared to canines and premolars. All participants indicated that they would not change to a different restorative protocol in order to have a thicker restoration and possibly less risk of fracture. Conclusion: Ultrathin ceramic veneers are a viable cosmetic dentistry treatment option that involve minimal or no tooth preparation. However, a tendency for increased early fractures was observed in the min-prep group.

Purpose: To compare trueness and precision between conventional and digital facial measurements and to evaluate the accuracy of different superimposition techniques for facial scans. Materials and Methods: Twenty volunteers were recruited. Predetermined facial landmarks were marked with a black marker, and the interlandmark distances were measured manually with a conventional caliper and digitally with Geomagic software. Two consecutive facial scans were performed and then superimposed, using as best-fit reference the full face, the face without the eyes, and the bone-supported areas (eg, forehead and zygomatic areas) in order to assess root mean square (RMS) differences. Trueness and precision were evaluated and compared between the conventional and digital techniques. Mann-Whitney U and Kruskal-Wallis post hoc tests were used. The significance level was established as α = .05. Results: Trueness between conventional and digital measurements was 1,151.75 ± 1,265.52 μm (3.04% ± 4.82%), and precision was 322.31 ± 300.54 μm (0.93% ± 1.10%). Global mean RMS values for each superimposition technique were 334.15 ± 172.07 for the full face, 339.57 ± 173.13 for the face without the eyes, and 385.65 ± 182.29 for the bone-supported areas, with the latter presenting statistically significant differences compared to the other two. Conclusion: Although statistically significant differences were detected in facial measurements, they were below the clinically detectable threshold. Superimposition with the full face and the face without the eyes area presented smaller discrepancies than with the bone-supported areas, with higher discrepancies in the lower third of the face.

Purpose: To evaluate whether a concordance assessment (CA) software application is able to assess decisionmaking in restorative and prosthetic dentistry. Materials and Methods: Vignettes representing 10 different clinical situations were integrated into a software application. Each vignette included 3D digital models and a short case, as well as 5 therapeutic options rated on a 4-point Likert scale (–2 = strongly contraindicated; –1 = contraindicated; +1 = indicated; +2 = strongly indicated). A panel of 15 dental educators (9 educators from a department of prosthetic dentistry [PD] and 6 from a department of conservative dentistry [CD]) evaluated the indication of each of the 5 therapies for the 10 vignettes. Results: This pilot questionnaire showed good internal consistency in most therapies (Cronbach’s α = 0.86), with the exception of more recently introduced therapies (overlay/veneerlay and endocrown). Out of a maximum score of 100, the mean score for CD educators (79.2 ± 3.2) was not significantly different (P = .73) from that of a PD educator (77.8 ± 3.5). Scores ranged from 66.8 to 89.6. Analysis of the expert panel’s responses also mostly reported (34/50) a distribution of responses that was characteristic of CA and uncertain situations. Conclusion: The present software application was able to reproduce and assess decision-making in dentistry with satisfying internal consistency of educators.

Purpose: To investigate and compare the production tolerances of six different commercially available implant scan bodies (SBs), with the null hypothesis that there would be no tolerances or significant differences between the different SBs. Materials and Methods: Six different implant SBs (IO 6A-B and IO 2B-B, Nobel Biocare; RC 4.1 mm 025.4915 and RN 4.8 mm 048.168, Straumann; KR 352KR1A0, BTK Dental Implants; and AANISR4013T, MegaGen) were evaluated. Five specimens of each SB type (total N = 30 samples) were screwed onto the corresponding implant analogs and underwent dimensional analysis with optical microscopy (QVI Smartscope Flash 200, Optical Gaging Products) and precision probing (R 0.25, Renishaw). The outcome variables were SB height, diameter, and angle of the flat face on the top (plane). All measurements were compared to the corresponding computer-assisted design library measurements as a reference to assess the tolerances. Statistical analyses were performed to compare the results obtained with the different SBs. Results: Tolerances in the manufacturing of the SBs were reported in height, diameter, and plane measurements, and statistically significant differences between the different types of SBs were found. Therefore, the null hypothesis was rejected. Most of the deviations and tolerances were reported in height measurements with conical connection implants. Conclusions: Production tolerances and statistically significant differences were found among the six commercially available SBs evaluated in this study. Additional studies with larger sample sizes and other types of SBs are needed.

Purpose: To evaluate the trueness of digital impressions of different composite resin materials that can be used for core buildups in clinical practice. Materials and Methods: A maxillary central incisor was prepared and scanned with an intraoral scanner (Primescan, Dentsply Sirona). Ten composite resin specimens (in three groups: universal composite; flowable composite; and bulk fill composite) were milled in the same dimensions of the prepared tooth and scanned. The data of the prepared tooth were used as reference, and the data obtained from the composite resin specimens were aligned using an evaluation software (Geomagic Studio 12) to determine deviation values. Kruskal-Wallis with Dunn post hoc test was performed to compare differences among the composite resin groups (α = .05). Results: There were significant differences in the trueness of digital impressions between some composite resin groups (P < .05). The mean trueness deviation values were in the range of 12.75 μm (G-aenial Posterior) to 17.06 μm (Filtek Bulk Fill Posterior). The trueness of G-aenial Posterior (12.75 μm) was higher than that of Core-X Flow (14.62 μm), Clearfil Majesty Flow (16.93 μm), and Filtek Bulk Fill Posterior (17.06 μm). Filtek Bulk Fill Posterior exhibited lower trueness than Clearfil Majesty Esthetic (12.93 μm), Clearfil Majesty Posterior (13.50 μm), and Charisma Classic (13.81 μm). Conclusion: Different composite resins used for core buildup can impact the trueness of digital impressions, with universal composite resin scans being the truest compared to flowable and bulk fill composite resin scans. All scanned substrate groups can be regarded as within a clinically acceptable range.

Purpose: To analyze the load to failure of different CAD/CAM high-density polymers (HDPs) and zirconia when titanium (Ti) bases were included in a cantilevered situation. Materials and Methods: Five specimens were fabricated from five different CAD/CAM polymethyl methacrylate (PMMA) HDPs (Copratemp [CT]; Tempo-CAD [TC]; Solid Shade PMMA Disc [TD]; M-PM Disc pink [MPM]; M-PM Disc white [MPMW]), and five specimens were prepared from an yttrium-stabilized tetragonal zirconia (3Y-TZP; FireZr [FZR]; control). Ti bases (D Master Dental Implants) were cemented onto the specimens (8 mm thick × 7 mm wide × 30 mm long). Each specimen was fixated using a clamp for a cantilever loading distance of 10 mm. The load was applied on the cantilever until failure, and the maximum load to failure values (N) were analyzed using analysis of variance (GLIMMIX procedure) with a log-normal error distribution in addition to the restricted maximum likelihood estimation method to eliminate the need for equality of variances and Tukey Honest Significant Difference test (α = .05). Results: Differences among the load-to-failure values of HDPs were not significant (P > .05); however, zirconia had significantly higher load-to-failure values than HDPs (P < .001). The behavior of HDPs and zirconia under loading was different in terms of displacement. HDPs showed weaker but more ductile behavior than zirconia, which is stronger, but more brittle. Conclusion: The tested brands of HDPs performed similarly under loading. Zirconia with a Ti base showed higher strength compared to all tested HDPs with a Ti base. The loads that fractured the specimens with Ti bases were close to the maximum occlusal bite forces recorded in previous clinical studies.

Purpose: To evaluate the mechanical stability and complication rates of titanium (Ti) and zirconia (Zr) abutments restored with cantilevered fixed dental prostheses (cFDPs) when supported by one or two implants.  Materials and Methods: A total of 32 specimens were fabricated. Half of the specimens received one implant, and the other half received two implants to simulate the clinical situation of two or three missing maxillary incisors, respectively. Each group was divided into two subgroups (n = 8). The Ti-1 and Ti-2 groups received Ti abutments (Anatomic Abutment, Straumann) supporting two- or three-unit metal cFDPs, respectively, while Zr-1 and Zr-2 groups received Zr abutments (IPS e.max Anatomic Abutment, Straumann). Following the cementation of cFDPs using resin cement (Multilink Automix, Ivoclar Vivadent), the specimens were subjected to thermomechanical fatigue load and then subsequently loaded until fracture in a universal testing machine. Following the static loading test, stereomicroscopic analyses (Carl Zeiss) were done to identify the weakest component of the cFDP, abutment, and implant assembly. Mann-Whitney U test was used to evaluate the effect of the number of supporting implants and abutment material on fracture strength values, and the level of statistical significance was set at 5% (α = .05). Results: All specimens survived aging, and no screw loosening or fracture was recorded. The mean fracture strength values were 226 N (± 26.45), 551.12 N (± 82.19), 601 N (± 41.51), and 664.5 N (± 37.59) for Zr-1, Zr-2, Ti-1, and Ti-2, respectively. The difference between fracture strength values of the Ti and Zr groups was significant in favor of Ti abutments (P < .001). The number of supporting implants showed a significantly positive effect on the fracture strength of Zr abutments. Conclusion: Zr abutments demonstrated lower fracture strength values than Ti abutments independent from the number of supporting implants when used under cFDPs. Two implant–supported cFDPs with zirconia abutments have the potential to withstand physiologic forces applied in the anterior region.

Purpose: To investigate and compare the degree of Streptococcus mutans (SM) colonization before and after in vitro wear simulation on monolithic zirconia (MZ), lithium disilicate (LD), ceramo-metal (CM), and composite resin (CR) specimens. Materials and Methods: Sixteen circular discs (10 × 3 mm) were fabricated for each group (MZ, LD, CR, CM). Half of the samples from each group (n = 8) were subjected to a wear cycle (n = 32 in total). The wild-type SM bacteria was incubated, diluted, and cultured for growth on the specimens with polished (n = 32) and worn surfaces (n = 32). The number of bacteria was calculated from colony-forming units (CFU). ANOVA followed by Tukey honest significant difference test (α < .05) was used for statistics. Results: SM adhesion on the polished surfaces of all the tested materials exhibited similar values (P = .215), with the number of SM being lowest for LD (21.87 ± 28.14) and highest for CM (90.62 ± 76.69). After the wear cycle, ANOVA indicated significant differences (P = .000) for the number of bacteria between pre- and postwear conditions of all groups. MZ (21,028 ± 1,507.98) and CM (13,025 ± 2,690.85) showed the highest and lowest numbers of SM colonies, respectively. According to t test, postwear SM adhesion to all materials (P = .000) was significantly higher. SM colonization on the worn surfaces of all the materials showed significant differences (P < .05), except for between LD and CR (P = .973). Conclusion: Polished surfaces of evaluated materials showed similar SM colonization, which emphasizes the importance of following the minimum requirements of the polishing/glazing procedures. SM colonization on the material surfaces significantly increased after wear. MZ and CM possessed the highest and lowest SM colonizations, respectively.

Purpose: To design and analyze the biologic properties (antibacterial and antifungal, as well as cytotoxicity) of a dental biomaterial based on incorporation of the biocide poly(diallyldimethylammonium chloride) (PDADMAC) into the masses of self- and thermopolymerizable acrylic resins. Materials and Methods: PDADMAC was diluted into tetrahydrofuran (4 wt%) and incorporated into self- and thermopolymerizable acrylic resins. PDADMAC inclusion was verified by measuring the contact angle with water droplets. Plain resins were used as controls. The antibacterial activity was evaluated against Staphylococcus aureus (ATCC 6538P) and Escherichia coli (ATCC 8739), and the antifungal activity was tested against Candida albicans (ATCC 10231) and Aspergillus niger (ATCC 16404). The cytotoxicity of substances leached from these materials was analyzed in human dental pulp stem cells using MTT reduction assay. Results: Reduction of contact angle confirmed the incorporation of PDADMAC in the resins. Both resins containing PDADMAC were more effective against Gram-positive and Gram-negative bacteria than their controls. The modified resins were also significantly more effective against Candida albicans than controls, but no resin was effective against Aspergillus niger. The cell viability of cultures submitted to substances leached from the PDADMAC resins was similar to that of cells cultured under ideal conditions. Conclusion: The incorporation of PDADMAC into the acrylic resins achieved the desired antibacterial effect, with no changes in the biocompatibility properties of the resins. Moreover, the modified resins were effective against Candida albicans, the most common fungus in the oral cavity. Thus, the incorporation of PDADMAC in biomaterials seems to be promising in dentistry

Purpose: To compare the precision of adaptation of cobalt-chromium (Co-Cr) three-unit fixed dental prostheses (FDPs) fabricated using different techniques. Materials and Methods: A master model was prepared to receive a three-unit FDP. This model was duplicated 60 times from a silicone mold. The dies (N = 60) were scanned and divided into three groups (n = 20 each) to receive FDPs made of presintered Co-Cr (CS), laser-sintered Co-Cr (LS), or cast Co-Cr (Gi). Frameworks were layered with ceramic, and each framework was seated on its specific model. The replica technique was used to measure the marginal and internal discrepancies in the mesiodistal and buccolingual planes. Prepared silicone samples were examined with scanning electron microscopy. Obtained data were analyzed using Levene test, t test, and analysis of variance (α = .05). Results: When overall mean discrepancy values were compared in the mesiodistal plane, LS showed better adaptation than Gi (P = .025). Similar adaptation was found for CS and Gi, and for CS and LS (P = .169 and P = 1.000, respectively). In the buccolingual plane, the difference in fit was not significant among the three tested groups (P > .05). In a pairwise comparison between materials, a net increase in discrepancy values was noted between measurement points 1 and 5 (P = .57). Differences in discrepancy values within points were significant. This was confirmed at the abutment level on some measurement points. Within each material, differences were significant at several measurement locations at the abutment level in both the mesiodistal and buccolingual planes. Conclusion: Within the limitations of this study, three-unit Co- Cr FDPs showed similar marginal and internal discrepancy values. Presintered and laser-sintered Co-Cr alloys can be considered for three-unit FDP fabrication.

Purpose: To systematically review all in vitro studies focusing on the durability of different bonding protocols applied to zirconia restorations with different types of tooth or implant abutments. Materials and Methods: English-language articles published in dental journals up to March 2020 were searched using a combination of free text words and MeSH terms, as follows: zirconia; Y-TZP; zirconium; zirconia restoration; enamel; dentin; titanium abutment; titanium base; ceramic abutment; dental core; ceramic or metal post and core; composite build-up; bonding; adhesive cement; resin cement; adhesion; cementation; test; material testing; laboratory; and in vitro. Studies were identified for review based on certain inclusion and exclusion criteria. Results: A total of 3,339 titles were identified. After a successive filtering process, a final total of 28 studies were included. The included studies featured different types of surface pretreatment methods, primers, resin cements, tooth and implant abutments, laboratory test outcomes, and designs. The relatively limited number of the identified studies and the heterogeneity of the extracted data did not allow for meta-analysis. Conclusions: Zirconia surface pretreatment is an essential step in the bonding protocol. Airborne-particle abrasion surface pretreatment had a positive influence on zirconia resin bonding to most types of tooth and implant abutments identified. Chemically activating the treated zirconia surfaces with an MDP monomer-based primer, along with an MDP monomer or phosphate ester monomer-based resin cement, seems to be a durable bonding protocol. Type of resin cement seems to be a less influential factor.

The present clinical report describes a treatment strategy for transition from full-arch restorations supported either partially or fully by failing implants that need to be removed. More specifically, the staged approach proposes a deferred treatment sequence in which the failing implants or teeth are not all replaced simultaneously. With this technique, some failing natural or artificial abutments are preserved momentarily in order to maintain the patient with a fixed provisional restoration at all times throughout the execution of treatment, from the surgical phase until delivery of the final restoration. The present clinical report describes the staged approach in detail, compares it to other treatment options, and illustrates all phases of therapy with a clinical case.