The International Journal of Prosthodontics, 04/2021

Purpose: To compare the rest vertical dimension (RVD) and occlusal vertical dimension (OVD) measurements obtained using a facial scanner with conventional methods and to evaluate the influence of the file format on the accuracy of the digital calculations. Materials and methods: Participants (N = 30) received marks on the glabella (Gb), tip of the nose (TN), and pogonion (Pg). Interlandmark distances Gb-TN and TN-Pg in the OVD and RVD positions were recorded by two operators conventionally (manual group) and digitally (digital group). For the manual group, measurements were obtained using a caliper. For the digital group, 10 scans in each position were obtained using a facial scanner (Face Camera Pro, Bellus3D) and exported in tessellation with polygonal faces (OBJ) and standard tessellation language (STL) file formats. Digital measurements were performed using both facial scan file formats and a software (Matera 2.4, exocad). The interocclusal rest distance (IRD) and the intraclass correlation coefficient were calculated. Shapiro-Wilk test was used to determine normal distribution. An independent samples t test, one-way analysis of variance, and post hoc Tukey test were used for analyses (± = .05). Results: No significant differences were found between the manual and digital measurements using the OBJ files or digital measurements using the STL files (P > .05). The IRD ranged from 0.72 ± 0.48 mm to 5.00 ± 1.34 mm. The inter- and intra-operator reliability were significant (P < .001), with a Cronbach's alpha value ranging from .994 to .997. Conclusion: No difference was found between manual and digital measurements. A high measurement consistency was encountered for each operator and between the operators. The facial scan file format did not influence the digital measurements.

Purpose: To evaluate the efficacy of two traditional acupuncture protocols on pain relief in temporomandibular disorder (TMD) patients using either local or distal acupoints for mechanical needle stimulation. Materials and methods: The sample was selected from female TMD patients with chronic pain from a specialized referral center. Clinical charts were retrieved to select patients treated by traditional acupuncture following either a protocol for application of needles in local acupoints (head, neck) or a protocol for application in distal acupoints (hands, legs, feet). Pain intensity was recorded before and after each acupuncture session by using an instrumental question with a 10-point visual analog scale (VAS). A control group consisted of nontreated patients from the waiting list for TMD treatment. Data were analyzed using descriptive statistics, paired t test, analysis of variance, and Tukey test, at a significance level of .05. Results: Out of 102 TMD patients, 32 were treated with acupuncture at local points, 22 were treated with acupuncture at distal points, and 48 were controls. A significant decrease of mean VAS score (approximately 70%) was found after acupuncture treatments in both the local- and distal-point groups. The final VAS of each acupuncture group was lower than the control group, but the acupuncture groups showed no difference. Conclusion: It can be concluded that acupuncture treatment reduces chronic pain in TMD patients, and the application of needle stimulation at local or distal acupoints has similar effects.

Purpose: To clinically evaluate oral implant restorations placed by undergraduate students in the dental clinical curriculum at KU Leuven (Belgium) in terms of function and esthetics. Materials and methods: A retrospective observational cohort study was designed. The esthetic and functional evaluations of implant-supported restorations placed in the framework of the undergraduate implant dentistry clinical training program using White/Pink Esthetic Score (WES/PES) and visual analog scale (VAS) scoring was performed. Furthermore, complications were registered based retrospectively on the patient's medical file. The following research questions were stipulated: (1) How well do implant-supported restorations placed by undergraduate students perform esthetically? and (2) Which complications occurred and how were these managed? Results: Between August 2008 and July 2014 (6 academic terms), 251 implants (Brånemark System Mk III, Nobel Biocare) were placed in 113 patients by 155 students (> 40% of all students enrolled in the training program). Of these implants, 228 were restored in 101 patients by 118 students with varying restoration types. Esthetic scoring of the restorations in 83 of these patients revealed a satisfying mean WES of 8.14 ± 2.09 (out of 10) and PES of 9.56 ± 3.14 (out of 14). Complications were registered in 18.9% of the cases. Discussion: Clinical training in implant dentistry for undergraduates contributes to the development of advanced skills in the dental student's Master education. Overall, patients were satisfied with their implant-supported restorations. Implant and restoration success rates and complication incidence were confirmed by long-term data in the oral implant literature.

Purpose: To assess the impact of different types of dental prostheses, including definitive and interim restorations, on oral health-related quality of life (OHRQoL) before and after prosthetic treatment. Materials and methods: A total of 151 patients received prosthetic treatment at one of two German departments of prosthetic dentistry. The patients' OHRQoL was assessed using the German version of the Oral Health Impact Profile (OHIP-G53) at baseline (T0) and at 1 week (T1) and 3 months (T2) after treatment. Patients were divided into 10 subgroups according to their pre- and posttreatment status. The effect of the type (no prosthesis; fixed prosthesis; removable prosthesis) and duration of wear (definitive; interim) of the restorations was evaluated. Results were analyzed using Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests with a significance level of P = .05. Results: The highest OHRQoL was recorded for patients with fixed restorations, as indicated by the fact that their OHIP scores were lowest. A significant improvement in OHRQoL (P ≤ .034) was observed for patients who needed prostheses and were then treated with removable or fixed restorations. The OHIP score was affected by a change in restoration type. Rehabilitation with definitive prostheses had a significant effect on posttreatment OHRQoL (P ≤ .006). Conclusion: In general, prosthetic rehabilitation by use of fixed or removable prostheses resulted in an improvement in OHRQoL. The use of the same type of restoration before and after treatment had a positive effect on OHRQoL. If possible, a change of restoration type should be avoided. For patients who require permanent prostheses, the use of fixed and removable restorations is recommended. For oral rehabilitation, fixed restorations should be preferred in order to achieve best possible improvement of OHIP score.

Purpose: To investigate the effect of monolithic zirconia-based occlusal surfaces on signs and symptoms of temporomandibular disorders (TMD) after short-term clinical service. Materials and methods: Patients were supplied with multi-unit fixed dental prostheses (FDP) featuring monolithic zirconia-based occlusal surfaces. Prior to prosthetic treatment and 1 year after insertion anamnestic facial pain, pain with palpation of muscles/joints and joint sounds were examined. Results: Of the 50 patients, 43 were re-examined after 1 year. Perceived facial pain was not present, pain with palpation occurred in 2 patients, and TMJ sounds decreased; differences were not statistically significant (P ≥ .058). Conclusion: Single tooth-supported multiunit FDPs featuring monolithic zirconia-based occlusal surfaces did not affect TMD-associated signs and symptoms.

Purpose: To evaluate the influence of repetitive autoclaving on diamond burs fabricated via different methods. Materials and methods: A total of 96 diamond burs were divided into 12 groups according to fabrication method (single-element electroplating, multi-element electroplating, or brazing) and number of times autoclaved (0, 5, 10, or 15). The surface characteristics and components of the diamond burs were examined using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The cutting efficiency of the diamond burs was tested with a constant-pressure cutting appliance. Results: Compared to the nonautoclaved group, the cutting efficiency of the multi-element and single-element electroplated diamond burs decreased significantly after autoclaving 5, 10, and 15 times (P < .05). The cutting efficiency of the brazed diamond burs started to decrease significantly after 10 cycles (P < .05). Cracks appeared on the surfaces of multi-element electroplated diamond burs after 10 and 15 cycles, but were absent in the single-element electroplated and brazed diamond burs. A reduction of nickel was detected in the multi-element electroplated and brazed diamond burs, but not in the single-element electroplated diamond burs. Conclusion: Repetitive autoclaving could reduce the cutting efficiency of diamond burs. The extent of the reduction was related to fabrication method and number of autoclaving times, suggesting that used diamond burs should be separately autoclaved to avoid shortening the life spans of unused ones.

Purpose: To investigate the impact of different extents of misfit between a restoration and the supporting implant on veneer fractures in screw-retained implant-supported metal-ceramic fixed dental prostheses (FDPs). Materials and methods: A finite element analysis (FEA) model of a five-unit screw-retained metal-ceramic FDP supported by three implants was constructed, replicating a previous in vitro study. Eight different gap configurations at the single terminal implant, ranging from 0 to 150 μm, were tested. All setups were tested after clamping and with a load of 200 N applied. Maximum stress within the FDP was calculated. Results: The stress increased with each increase in misfit size above 30 μm, with the relationship between gap size and stress being linear up to 100-μm misfit. Above 100 μm, the stress increase accelerated. The stress pattern within the FDP changed with increasing gap size, confirming the findings of a previously conducted in vitro experiment for a misfit of 150 μm. Conclusion: The results of the FEA were in agreement with in vitro observations, validating the predictive value of FEA for technical complications. A misfit between an FDP and a supporting implant implies an increased risk of veneer fracture. Above a misfit of 30 μm, the stress levels are likely to be high enough to cause veneer fracture, and the risk increases disproportionately for misfit above 100 μm.

Purpose: To explore the effect of in situ synthesized particulates on a zirconia surface on the bonding properties between zirconia and porcelain. Materials and methods: Presintered yttrium-stabilized tetragonal zirconia (Y-TZP) was cut into slices and bars and polished with 1,200-grit silicon carbide abrasive paper. Samples were randomly divided into six groups (C, I₁, I₃, I₅, I₇, and I₉) according to immersion time in hydrofluoric acid solution (0, 10, 30, 50, 70, and 90 seconds, respectively). Then, the samples were placed in calcium chloride solution for 90 seconds and dipped in sodium hydroxide solution at 80°C for 2 hours. After sintering, the surface topography and roughness were examined. After the porcelain was fired, the bonding interface was observed, and cross-sectional microhardness was measured. The shear bond strength of the zirconia to porcelain was evaluated, and failure modes were classified. A 3-point bending test was applied to confirm the effects of the treatment on the mechanical properties. The above data were statistically analyzed. Results: Polycrystalline particulates were synthesized on the zirconia surface. The surface roughness values increased as the immersion time of the samples in hydrofluoric acid increased. The cross-sectional microhardness decreased gradually in the experimental groups. Group I₇ showed an elevated bond strength (27.02 ± 2.44 MPa). Mainly mixed failure mode was obtained in the experimental groups. The Weibull characteristic strength for the experimental groups was higher than that of group C. The flexural strengths were not significantly different among the groups. Conclusions: In situ synthesized polycrystalline particulates on zirconia could effectively improve the bonding between zirconia ceramics and porcelain without significantly decreasing the mechanical properties.

Purpose: To determine the effects of tooth brushing on the surface roughness (Sa) and morphology, maximum relative depth (Rv), gloss (GU), and microhardness (MH) of four esthetic restorative materials and enamel. Materials and methods: A light-curing composite resin (Filtek Supreme Ultra [FSU], 3M ESPE), two hybrid resin/ceramic CAD/CAM materials (Lava Ultimate [LAV], 3M ESPE, and VITA Enamic [VEN], VITA Zahnfabrik), and a CAD/CAM feldspathic ceramic (VITA Blocs Mark II [VMA], VITA Zahnfabrik) were evaluated. Bovine enamel (ENA) was used as a control group. All surfaces were polished in accordance with the manufacturer's instructions. Samples were analyzed before and after brushing (30,000 cycles) regarding Sa and Rv using a 3D laser-measuring microscope. GU was evaluated every 10,000 tooth brushing cycles. MH was also measured before and after tooth brushing. The surfaces were observed using scanning electron and laser measuring microscopies to determine the wear patterns. Data were analyzed by paired t test, one-way or two-way repeated measures analysis of variance, and Tukey test (α = .05), depending on the method performed. Results: The Sa increased significantly after brushing for all materials, except for VMA, which showed the opposite effect. ENA and VEN showed higher Rv than VMA. After 30,000 tooth brushing cycles, VMA showed the highest GU, while FSU showed the lowest. Also, little surface topography changes were observed for VMA. MH did not change significantly after 30,000 brushing cycles, except for LAV. Conclusion: Brushing caused surface alterations in all tested materials except for feldspathic ceramic. The changes were more evident in resin-based materials.

Purpose: To assess the clinical outcomes of maxillary overdentures supported by dental implants by conducting a literature review. Materials and methods: An electronic search was undertaken in March 2019. Eligibility criteria included publications reporting cases of implant-supported maxillary overdentures with follow-up information. Results: A total of 131 publications were included (1,478 overdentures supported by 6,681 implants). The mean number of attachments per overdenture was 3.8 ± 1.2 (range: 1 to 9), and a bar-clip system was used in about half of the cases. The prostheses were followed up for a mean of 47.9 ± 32.8 (range 1: to 240) months. A total of 401 implants (6.0%) failed in 219 patients (14.8%), and 55 prostheses (3.7%) failed at a mean of 40.2 ± 53.2 (6 to 240) months after placement. Most of the failures happened within the first year after placement for both implants (52.1%) and prostheses (41.8%). Patients with fewer implants per prosthesis presented higher prosthesis failure rates than patients with more implants per prosthesis. The cumulative survival rate for dental implants after 19 years was 70.4%, and for implant-supported maxillary overdentures was 79.8%. Presence of palatal coverage and/or metallic structure/reinforcement does not seem to have an influence on failure rate. Of the most commonly used attachment systems, the ball/O-ring and the Ceka were the ones with the highest rates of patients having at least one implant failure. Conclusion: Most of the prosthesis failures were due to loss of implants, and the first year was the most critical period for failures. The number of dental implants placed per patient seemed to have an impact on the occurrence of overdenture failure.

Purpose: To evaluate the wear of zirconia on natural teeth in humans in vitro and in vivo. Materials and methods: Embase, the Cochrane Database, PubMed, and the Web of Science were searched (January 2014 to May 2019), and all references were retrieved. After preliminary screening of the literature, two researchers read the full texts of the remaining literature and determined whether the literature should be included. Data and information were extracted from the included literature, then analyzed and discussed. Results: A total of 49 in vivo experiments and 229 in vitro experiments were retrieved. After duplication removal and screening, 7 in vivo studies and 13 in vitro studies were included. The results of the in vitro studies showed that fine polished zirconia causes less antagonist wear on natural teeth than other treatments with zirconia or other restorative materials. The results of the in vivo studies showed the antagonist wear of zirconia on natural teeth was within the clinically acceptable range. Conclusion: Both in vivo and in vitro studies have shown polishing can reduce the wear of zirconia on natural teeth more than glazed or veneering porcelain. However, whether glazed zirconia causes less natural tooth wear after polishing is still a matter of debate. Due to the short observation period and heterogeneity of the experiment, the above conclusions should be carefully interpreted.

Purpose: To evaluate the effect of build direction on the surface roughness (Ra) of stereolithography (SLA) printed full-coverage anterior dental restorations before and after surface polishing. Materials and methods: A total of 45 full-coverage dental restorations were 3D printed using the SLA additive manufacturing technique. Five groups were defined based on the build angles: 90, 120, 135, 150, and 180 degrees. The Ra was measured with the contact profilometer to evaluate the arithmetic average of the absolute Ra value on the labial surface before and after polishing procedures. Data were analyzed using two-way ANOVA, and statistical significance was set at α = .05. Results: The highest Ra was recorded in specimens printed with the 90-degree build angle, whereas the lowest values were recorded in specimens printed with the 180-degree build angle (P = .000). In all groups, the Ra values measured after polishing were significantly lower than prepolished values (P = .000), with no difference among the different build angles. Conclusion: Build angle significantly influenced the Ra of the SLA-printed full-coverage restorations. Polishing minimized the effect of build angle on the Ra. The 180-degree build angle is recommended when SLA printing an anterior restoration, as it provides the lowest Ra values and also requires a minimal support area and minimal number of support structures.

Purpose: To investigate the differences in accuracy (trueness and precision) of five different optical impression systems. Materials and methods: The accuracy of the following optical impression systems was tested: (1) CEREC Bluecam (BL; Dentsply Sirona), (2) CEREC Omnicam (OM, Dentsply Sirona); (3) PlanScan (PL; Planmeca); (4) True Definition Scanner (TD; 3M ESPE); and (5) Trios 3 (TR; 3Shape). A standard plastic study model represented a patient with a fully dentate maxilla (ANA-4 V CER, frasaco). Three clinical situations were simulated: Patient 1 (P1): fully dentate; Patient 2 (P2): anterior partial edentulism (two missing incisors); and Patient 3 (P3): posterior partial edentulism (P3) (missing premolar and molar). The models were scanned with a reference scanner (IScan D104i, Imetric), and the digitalized models were used as reference for all comparisons. Then, optical impressions were made for the three clinical scenarios (n = 10 per group). Results: In situation P1, the TD group provided the highest trueness (180.2 ± 46.3μm). In situation P2, the highest trueness was found in the TD (97.9 ± 27.6 μm) and TR (105 ± 9.5μm) groups, and in situation P3, TR had the highest trueness (P < .05) with a median RMS value of 76.2 ± 5.6 μm. In terms of precision, TR provided the highest precision (P < .05) in all three clinical situations, with RMS values 76.7 ± 26 μm for P1, 46.8 ± 14.1 μm for P2, and 39.7 ± 9.1 μm for P3. Conclusion: Two optical impression systems (TR and TD) were superior to the other tested systems in most of the measurements. However, none of the tested systems was clearly superior with respect to both trueness and precision.

Monolithic zirconia implant-supported restorations connected to titanium bases or titanium inserts are increasing in popularity due to their application in a full digital workflow. These prefabricated abutments are connected to the all-ceramic superstructure by adhesive cementation. Although limited clinical data on the outcomes of this type of restoration are available, a few laboratory studies have shown possible debonding issues. This case report presents a bonding failure of a fixed dental prosthesis supported by titanium bases after short clinical use. A treatment alternative is also proposed using the available digital dental technology.