The International Journal of Prosthodontics, 01/2023

Purpose: To evaluate the minimum ceramic thickness needed to increase the lightness by one value by means of glass-ceramic restorations, as perceived by dental technicians, dentists, and laypersons. Materials and Methods: A total of 15 assessment pairs (= reference and test sample) were formed using glass-ceramic blocks in four different colors. Each assessment pair was comprised of two underground blocks differing by one value of lightness. On top of the underground blocks, glass-ceramic platelets were cemented in 5 different thicknesses (0.1 to 0.5 mm) in the same color as the reference. Dental technicians, dentists, and laypersons (n = 41/group) were asked to determine the presence of a color difference between the two samples under standardized light conditions. The threshold ceramic thickness was defined as the thickness at which ≥ 50% of the evaluators were not able to perceive a difference within an assessment pair. The thresholds were analyzed, and groups were compared by applying chi-square test (P < .05). Results: The majority of dentists and dental technicians (> 50%) detected a lightness difference between test and reference samples up to a ceramic thickness of 0.5 mm. The majority of laypersons (≥ 50%) did not perceive lightness differences with ceramic thicknesses of 0.5 mm. If separated by the different color changes, the threshold ceramic thickness started at 0.4 mm and varied within the groups of evaluators and the lightness of the assessed color. Conclusions: A considerable number of evaluators perceived a lightness difference when minimally invasive ceramic restorations of 0.5-mm thickness were applied. The threshold ceramic thickness, however, was reduced when the lightness of the substrate was lower.

Purpose: To compare patient adaptation to and satisfaction with new complete dentures fabricated via a duplication construction protocol (DCP) using two different occlusal schemes: bilateral balanced (BBO) and lingualized (LO). Materials and Methods: A total of 20 complete denture wearers who received replacement DCP dentures participated in this study. Of these, 10 participants received complete dentures with a BBO scheme, while the other 10 received DCP dentures with an LO scheme. All of them evaluated their prostheses subjectively through the Oral Health Impact Profile-20 (OHIP-20) and the Complete Denture Satisfaction (CDS) questionnaires before treatment and at 3- and 6-month posttreatment intervals. The new prostheses were also normatively evaluated by recording the location and number of sore spots present at the scheduled early adjustment visits. Data were analyzed with nonparametric tests to identify differences in patient response both between groups and within each group at each evaluation interval (α = .05). Results: The within-group comparisons revealed statistically significant improvement for both denture groups (P < .05), while the between-group comparisons did not show statistically significant differences at the overall evaluation period (P > .05). Significant within-group differences were recorded in the pain, functional limitation, and psychologic disability domains of the OHIP-20 questionnaire, as well as the comfort, esthetics, and stability domains of the CDS questionnaire. Conclusion: Patient adaptation to and satisfaction with newly constructed DCP dentures improved significantly for both BBO and LO denture groups throughout the evaluation period. The mean number of early adjustment visits was equal for both the BBO and LO denture groups.

Purpose: To measure the validity and reliability of two gingival shade guides used to represent in vivo gingival color in a Caucasian population sample. Materials and Methods: The CIELAB color space was used to study three gingival reference areas (the free gingival margin, the keratinized gingival body, and the upper part of the keratinized gingiva) in a sample of 259 Caucasian individuals. The color coordinates on the HeraCeram Gingiva and on the IPS d.SIGN physical gingival shade guides were collected to compare with the color coordinates taken in vivo. The coverage errors (CEs) of the two shade guides were calculated using the CIELAB and CIEDE2000 formulas, and each area of the gingiva was compared with the 50:50% acceptability thresholds of ΔE* = 4.6 and ΔE00* = 4.1, respectively. The SpectroShade spectrophotometer was used. Results: IPS d.SIGN showed similar CEs in all three areas and, in all cases, surpassed the 50:50% acceptability threshold. In contrast, HeraCeram Gingiva had a lower CE in the free gingival margin than in the other two areas, and the CE remained below the 50:50% acceptability threshold only for ΔE00*. The HeraCeram Gingiva shade guide had overall CEs (ΔE* = 7.9 and ΔE00* = 5.6) that were significantly lower than obtained for the IPS d.SIGN guide (ΔE* = 9.2 and ΔE00* = 6.8). Conclusion: Statistically significant differences were found in the CEs of both guides, both at the level of the three reference areas and at the global level. For both guides and in both genders, the global CEs calculated with the CIELAB and CIEDE2000 formulas were below the literature data on 50:50% acceptability thresholds.

Purpose: To evaluate the stress distribution during chewing in a realistic loading condition on a prosthesis (single-tooth crown) using a static analysis. Materials and Methods: An all-ceramic crown on the mandibular first molar was selected as the representative prosthesis. First, three contact states (intrusive state, transition state, and extrusive state) were selected from the parametric chewing trajectory. Then, the distance between the antagonistic molars and the normal vectors of the mandibular first molar were calculated by using an automated contact analysis routine (independently developed). Next, normal and tangential forces were defined based on the contact information and the food property. Finally, the static analysis was executed by applying the force and the fixed boundary condition. Results: The distribution of the occlusal force was nonuniform in the static analysis. Compared to concentrated and uniform loading conditions, the stress distribution of the prosthesis under the nonuniform loading condition revealed new characteristics. Conclusion: The generation procedure of the static analysis, based on fundamental contact analysis, was well founded. Static analysis with the nonuniform loading condition is more recommended than the other two conditions.

Purpose: To compare the load-to-failure values of different ceramic CAD/CAM implant crown materials with drilled screw-access holes with and without cyclic loading applied. Materials and Methods: Forty zirconia abutments with a titanium base were pre-loaded onto implants to support maxillary right first premolar crowns milled from four different CAD/CAM ceramic materials (zirconia-reinforced lithium silicate, hybrid ceramic, lithium disilicate, and zirconia; n = 10 each). After cementing the crowns, the screw-access channels were prepared by drilling through the occlusal surfaces. Half of the specimens were subjected to cyclic loading for 5 million cycles at 2 Hz (n = 5/material). After cyclic loading, vertical loads were applied until failure. The load-to-failure values of all crowns were recorded and statistically analyzed. Two-way ANOVA was used with restricted maximum likelihood estimation and Tukey-Kramer adjustments (α = .05). Results: During cyclic loading, the zirconia abutment under one lithium disilicate specimen cracked at 2 million cycles, and a zirconia-reinforced lithium silicate crown also fractured. Results for the load-to-failure test series showed statistical differences between the materials. Zirconia resulted in significantly higher failure loads when compared to the other materials (P < .001). Cyclic loading did not significantly affect the load-to-failure values. Conclusion: Cyclic loading did not significantly influence the load to failure of any of the materials tested. Zirconia crowns with drilled screw access channels cemented on zirconia abutments with a titanium base had higher load-to-failure values compared to the other ceramic crown materials.

Purpose: To evaluate the effect of different treatments applied to titanium implant abutment surfaces on the retention of implant-supported crowns retained using resin cement. Materials and Methods: A total of 72 titanium implant abutments were divided into six groups (n = 12 each) based on the selected surface treatment: (1) untreated; (2) sandblasted; (3) hydrogen peroxide–etched; (4) atmospheric plasma; (5) chemical mechanical polishing; and (6) titanium dioxide nanocoating. After the surface treatments, scanning electron microscopy analyses and roughness measurements of the abutment surfaces were performed. Then, 72 metal copings were fabricated and cemented onto the abutments with dual-curing resin cement. After the thermocycling process, crown retention was measured by using a universal testing machine. The experimental results were statistically evaluated with one-way analysis of variance, Tukey honest significant difference, and Tamhane T2 tests. Results: The highest surface roughness values were obtained in the sandblasted group (1.44 um), which also showed in the highest retention values (828.5 N), followed by the hydrogen peroxide etching group (490.7 N), the atmospheric plasma group (466.5 N), the chemical mechanical polishing group (410.8 N), and the control group (382.6 N). Conclusion: Sandblasting, hydrogen peroxide, etching, and atmospheric plasma treatments significantly increased crown retention, and all alternative treatments, with the exception of TiO2 nanocoating, worked better than the control samples.

Purpose: To analyze the influence of pristine matrix and O-ring dimensions on retention force and its reproducibility in single one-piece mini dental implants (MDIs) with ball patrices under in vitro conditions. Materials and Methods: Three different matrix/O-ring combinations (MH1, MH2, and MH3) were evaluated (n = 50 measurements each) on 1.8-mm–diameter implants. The matrices were manually mounted on the implants and subsequently removed in a vertical linear manner using a metal pin with two strain gauges, which recorded the maximum force during disconnection. The O-rings were exchanged after five disconnections, and the mean retention force was calculated, resulting in a total of 50 values for each matrix/O-ring combination. Mean and SD retention forces with 95% CI were calculated. ANOVA was used to test the global difference, and post hoc pairwise comparisons were subsequently applied. The level of significance was set at P < .05. Results: ANOVA (global P < .0001) and pairwise comparisons (all P < .001) demonstrated statistically significant differences between the three different matrix/O-ring combinations with mean values of 5.18 N (MH 1), 6.73 (MH 2), and 9.08 (MH 3). Within each combination, retention force variations of > 1 N could not be demonstrated; ie, by exchanging O-rings, a similar retention force can be reestablished. Conclusion: Matrix and O-ring dimensions have a significant influence on retention forces in one-piece MDIs. Pristine O-rings demonstrated highly reproducible initial retention forces in all matrices.

Purpose: To assess the influence of two preparation techniques on the microleakage, marginal fit, and cement thickness of lithium disilicate veneers. Materials and Methods: A total of 24 human maxillary central incisors were divided randomly into two groups according to preparation technique (n = 12 each): a minimally invasive preparation with a butt-joint design (0.3-mm depth) and a chamfer finish line (group MP); and no preparation (group NP). All teeth were restored with lithium disilicate veneers cemented with photopolymerizable resin cement. Specimens were aged thermally (6,000 cycles of 5ºC to 55ºC) and mechanically (100,000 cycles at 100 N, 4 Hz). Specimens were immersed in fuchsin dye for 24 hours using a standard dye penetration technique, then sectioned and evaluated under a stereomicroscope (×20 magnification). Data were analyzed by ANOVA and Kruskal-Wallis tests (P < .05). Results: There was significant microleakage (P = .0163) at the cervical area compared to the proximal area. The marginal fit was similar, with no statistical difference (P = .212) between groups MP (153 ± 81 μm) and NP (111 ± 74 μm). Group MP showed a significantly (P = .006) reduced cement thickness at the cervical area (87 ± 27 μm) compared to group NP (210 ± 89 μm). Conclusion: Although the preparation technique was shown to influence the cement thickness, it did not show any influence on microleakage or marginal fit.

This manuscript presents a more accurate methodology, in comparison to extant approaches, that enables errorless congruence between an implant scanbody and its counterparts in the scanbody library of a dental computer-aided design (CAD) application. The proposed method deletes corners and difficult intraoral scanning regions and selects only the remaining flat and wide scanbody planes in the library. Achieving overlap between the portions of the actual scanbody data without distortion using an intraoral scanner is a novel development that is expected to represent a new standard in scanbody library alignment.

This case report describes a new digital workflow for computer-assisted implant surgery in an edentulous patient using transitional implants to support a fixed surgical template and interim prosthesis. The accuracy of the final implant position using the described protocol was evaluated and compared to the outcomes obtained using other types of surgical templates. This novel digital approach appears to enhance the accuracy of implant positioning for edentulous patients and seems to be comparable to a tooth-supported surgical template.

Purpose: To evaluate the effects of acidic solutions on the surface roughness (SR) and surface microhardness (SMH) of indirect restorative materials by analyzing in vivo and in vitro studies. Materials and Methods: Studies comparing the SR and SMH of indirect restorative materials after erosion were included in the metaanalysis. Meta-analyses were conducted with a random-effects model at a significance level of P < .05 using Review Manager software (Cochrane Collaboration). The literature search was conducted using the Web of Science, MEDLINE (PubMed), and Cochrane Library databases, with no limitations on publication year. Results: Of the 1,097 potentially relevant studies, 32 full-text articles were assessed for eligibility. A total of 16 articles were included in the systematic review, and 15 were included in the meta-analyses. The kappa score between the two reviewers was 0.80. The effects of erosion on ceramics, indirect composites, and hybrid ceramics were evaluated by immersion in or rinsing with acidic solutions (eg, hydrochloric acid [HCl], cola drinks, and juices). An increase in the SR (Ra values) (P < .00001; mean difference [MD] = –0.04; 95% CI = –0.06 to –0.03) and a decrease in the SMH (Vickers microhardness [VHN]) (P < .00001; MD = 13.94; 95% CI = 12.33 to 15.55) were found after erosion. Subgroup analyses revealed that in vitro erosion led to significantly higher Ra values and lower VHN values than in vivo erosion; cola drinks and juices led to more surface degradation than HCl; and the SR and SMH of polymer-infiltrated ceramic network (PICN) materials remained unchanged after erosion. Conclusion: After acidic challenges, significantly increased surface roughness and decreased surface microhardness were found on the surfaces of indirect restorative materials. Among all the indirect restorative materials, PICN showed the best acid resistance. Nevertheless, the changes in the SR and SMH of indirect restorative materials after erosion detected in the present study were minor and may not have any clinical significance.

Purpose: To compare the marginal gap and internal fit of fixed dental prostheses (FDPs) fabricated using intraoral vs extraoral scanning methods. Materials and Methods: MEDLINE/PubMed and the Cochrane database were searched. The focused PICO question was: For the fabrication of FDPs, does an intraoral scanning technique result in a different marginal gap than an extraoral scanning technique? The secondary outcome assessed was internal fit. Studies were selected based on the inclusion criteria, and a meta-analysis was performed. Results: A total of 14 studies (10 in vitro and 4 in vivo) were included in the meta-analysis. Marginal gap in single crowns was evaluated in 5 studies, copings for single crowns in 5 studies, three-unit FDPs in 3 studies, and both single-crown and three-unit FDPs in 1 study. Significantly lower marginal gap was found with intraoral scanning compared to impression scanning (P < .001) and cast scanning (P < .001), and for impression scanning compared to cast scanning (P = .037). Internal fit was superior with intraoral scanning compared to impression scanning, and this difference was significant (P < .001). No significant differences were found in internal fit with cast scanning compared to intraoral or impression scanning. The mean marginal gap/internal fit was 188.3 μm/146.2 μm with intraoral scanning, 116.29 μm/168.2 μm with impression scanning, and 195.1 μm/229.1 μm with cast scanning. Conclusion: Marginal gap was lower with intraoral scanning than with impression scanning and cast scanning. Impression scanning showed less marginal gap than cast scanning. Internal fit with intraoral scanning was superior to impression scanning, but when compared to cast scanning, no difference was found.

Purpose: To provide a 1-year assessment of friction-retention abutments used to retain a single lithium disilicate (LS2) monolithic restoration. Materials and Methods: A total of 522 implants were placed to treat a mandibular or a maxillary single-tooth premolar or molar edentulous site. Three types of implants were used. The tested abutments were connected 3 months after implant placement. A single pressed LS2 monolithic restoration was cemented to a dedicated titanium cap and engaged to the abutment without the use of screws or cement. Any complications affecting the restoration or the opposing dentition, any soft tissue dimensional changes, the distance between the implant platform and the bone peak, and pocket probing depths were recorded at the time of restoration placement (T0), after 6 months of function (T1), and after 1 year of function (T2). Esthetic, functional, and biologic parameters were recorded at T0 and T2. Results: A total of 507 patients (284 women and 223 men) received a restoration at T0, and 504 reached the 1-year follow-up at T2. One restoration fractured after 10 months in function. No statistically significant differences were seen in the soft tissue measurements or in the measurements of the distance between the supporting implant platform and the bone peak. None of the restorations detached during the observation period. Conclusion: The friction retention abutment is a viable option to retain an implantsupported monolithic LS2 glass-ceramic restoration in cases of premolar or molar single-tooth edentulism.