Reconstruction of dental roots for implant planning purposes: a retrospective computational and radiographic assessment of single-implant cases

PURPOSE

The aim of the study was to assess the deviation between clinical implant axes (CIA) determined by a surgeon during preoperative planning and reconstructed tooth axes (RTA) of missing teeth which were automatically computed by a previously introduced anatomical SSM.

METHODS

For this purpose all available planning datasets of single-implant cases of our clinic, which were planned with coDiagnostix Version 9.9 between 2018 and 2021, were collected for retrospective investigation. Informed consent was obtained. First, the intraoral scans of implant patients were annotated and subsequently analyzed using the SSM. The RTA, computed by the SSM, was then projected into the preoperative planning dataset. The amount and direction of spatial deviation between RTA and CIA were then measured.

RESULTS

Thirty-five patients were implemented. The mean distance between the occlusal entry point of anterior and posterior implants and the RTA was 0.99 mm ± 0.78 mm and 1.19 mm ± 0.55, respectively. The mean angular deviation between the CIA of anterior and posterior implants and the RTA was 12.4° ± 3.85° and 5.27° ± 2.97° respectively. The deviations in anterior implant cases were systematic and could be corrected by computing a modified RTA (mRTA) with decreased deviations (0.99 mm ± 0.84 and 4.62° ± 1.95°). The safety distances of implants set along the (m)RTA to neighboring teeth were maintained in 30 of 35 cases.

CONCLUSION

The RTA estimated by the SSM revealed to be a viable implant axis for most of the posterior implant cases. As there are natural differences between the anatomical tooth axis and a desirable implant axis, modifications were necessary to correct the deviations which occurred in anterior implant cases. However, the presented approach is not applicable for clinical use and always requires manual optimization by the planning surgeon.

Root-analogue implants compared to forced orthodontic extrusion: a retrospective analysis of clinical, radiological and esthetic outcomes after restoration

OBJECTIVES

To assess clinical, radiological and esthetic outcomes of restorations supported by root-analogue implants (RAIs) or roots of severely damaged teeth after forced orthodontic extrusion (FOE).

MATERIALS AND METHODS

Clinical data regarding milled one-piece (titanium/zirconia roots and zirconia abutments) RAIs (REPLICATE™ System) and FOE were recorded and retrospectively evaluated for 40 patients by two investigators. Strict inclusion and exclusion criteria were applied. Functional and esthetic outcomes were assessed for n = 20 pre-molars and n = 20 anterior teeth via comparison of radiographic and digital images applying the novel Functional Implant Prosthodontic Score (FIPS). Krippendorff's alpha coefficient was calculated to assess inter-rater reliability. Mann-Whitney-U-Test was used to compare the assessed parameters. Level of significance was set to p < 0.05.

RESULTS

After a mean observation period of 18.4 ± 5.7 months for restorations supported by RAIs and 43.9 ± 16.4 months for restorations after FOE, mean FIPS scores were 9.2/8.8 ± 1.1/1.2 (RAIs) and 7.4/7.7 ± 1.3/1.5 (FOE), respectively. Krippendorff's alpha coefficients did not reveal unacceptable inter-rater reliabilities regarding the investigators and applicability of FIPS. Significant differences were documented when comparing restorations after FOE or supported by RAIs regarding bone loss (p < 0.01), presence of papillae (p < 0.05) and quality and quantity of mucosa (p < 0.02) in favor of FOE.

CONCLUSIONS

Within the main limitations of sample size and the retrospective study design, both concepts seem to provide clinically acceptable results.

CLINICAL RELEVANCE

Bone- and tissue-preserving characteristics regarding the concept of FOE are promising. It could be applicable for socket preservation and subsequent conventional implant placements in an adapted workflow.

Systematic review evaluating the influence of the prosthetic material and prosthetic design on the clinical outcomes of implant-supported multi-unit fixed dental prosthesis in the posterior area

OBJECTIVE

The objectives of the study were to assess the survival, failure, and technical complication rates of implant-supported fixed dental prosthesis (iFDPs) with pontic or splinted crown (iSp C) designs in the posterior area and compare the influence of prosthetic materials and prosthetic design on the outcomes.

METHODS

Electronic and manual searches were performed to identify randomized-, prospective-, and retrospective clinical trials with follow-up time of ≥12 months, evaluating the clinical outcomes of posterior iFDPs with pontic or iSp Cs. Survival and complication rates were analyzed using robust Poisson's regression models.

RESULTS

Thirty-two studies reporting on 42 study arms were included in the present systematic review. The meta-analysis of the included studies indicated estimated 3-year survival rates of 98.3% (95%CI: 95.6-99.3%) for porcelain-fused-to-metal (PFM) iFDPs, 97.5% (95%CI: 95.5-98.7%) for veneered zirconia (Zr) iFDPs with pontic, 98.9% (95%CI: 96.8-99.6%) for monolithic or micro-veneered zirconia iFDPs with pontic, and 97.0% (95%CI: 84.8-99.9%) for lithium disilicate iFDPs with pontics. The survival rates for different material combination showed no statistically significant differences. Veneered restorations, overall, showed significantly (p < .01) higher ceramic fracture and chipping rates compared with monolithic restorations. Furthermore, there was no significant difference in survival rates (98.3% [95%CI: 95.6-99.3%] vs. 99.1% [95%CI: 97.6-99.7%]) and overall complication rates between PFM iFDPs with pontic and PFM iSp Cs.

CONCLUSIONS

Based on the data identified by this systematic review, PFM, veneered Zr, and monolithic Zr iFDPs with pontic and iSp Cs showed similarly high short-term survival rates in the posterior area. Veneered restorations exhibit ceramic chipping more often than monolithic restorations, with the highest fracture rate reported for veneered Zr iFDPs.

Influence of planning software and surgical template design on the accuracy of static computer assisted implant surgery performed using surgical guides fabricated with material extrusion technology: An in vitro study

OBJECTIVES

This in vitro study aimed to assess the influence of the planning software and design of the surgical template on both trueness and precision of static computer assisted implant surgery (sCAIS) performed using surgical guides fabricated using material extrusion (ME).

METHODS

Three-dimensional radiographic and surface scans of a typodont were aligned using two planning software (coDiagnostiX, CDX; ImplantStudio, IST) to virtually position the two adjacent oral implants. Thereafter, surgical guides were created with either an original (O) or modified (M) design with reduced occlusal support and were steam sterilized. Forty surgical guides were used to instal 80 implants equally distributed among four groups: CDX-O, CDX-M, IST-O, and IST-M. Thereafter, the scan bodies were adapted to the implants and digitised. Finally, inspection software was used to assess discrepancies between the planned and final positions at the implant shoulder and main axis level. Multilevel mixed-effects generalised linear models were used for statistical analyses (p = 0.05).

RESULTS

In terms of trueness, the largest average vertical deviations (0.29 ± 0.07 mm) could be assessed for CDX-M. Overall, vertical errors were significantly dependent on the design (O < M; p ≤ 0.001). Furthermore, in horizontal direction, the largest mean discrepancy was 0.32 ± 0.09 mm (IST-O) and 0.31 ± 0.13 mm (CDX-M). CDX-O was superior compared to IST-O (p = 0.003) regarding horizontal trueness. The average deviations regarding the main implant axis ranged between 1.36 ± 0.41 ° (CDX-O) and 2.63 ± 0.87 ° (CDX-M). In terms of precision, mean standard deviation intervals of ≤ 0.12 mm (IST-O and -M) and ≤ 1.09 ° (CDX-M) were calculated.

CONCLUSIONS

Implant installation with clinically acceptable deviations is possible with ME surgical guides. Both evaluated variables affected trueness and precision with negligible differences.

CLINICAL SIGNIFICANCE

The planning system and design influenced the accuracy of implant installation using ME-based surgical guides. Nevertheless, discrepancies were ≤ 0.32 mm and ≤ 2.63 °, which may be considered within the range of clinical acceptance. ME should be further investigated as an alternative to the more expensive and time-consuming 3D printing technologies.

One-Piece Zirconia Oral Implants for the Support of Three-Unit Fixed Dental Prostheses: Three-Year Results from a Prospective Case Series

The objective was to investigate the clinical and radiological outcome of one-piece zirconia oral implants to support three-unit fixed dental prostheses (FDP) after three years in function. Twenty-seven patients were treated with a total of 54 implants in a one-stage surgery and immediate provisionalization. Standardized radiographs were taken at implant placement, after one year and after three years, to evaluate peri-implant bone loss. Soft-tissue parameters were also assessed. Linear mixed regression models as well as Wilcoxon Signed Rank tests were used for analyzing differences between groups and time points (p < 0.05). At the three-year evaluation, one implant was lost, resulting in a cumulative survival rate of 98.1%. The mean marginal bone loss amounted to 2.16 mm. An implant success grade I of 52% (bone loss of ≤2 mm) and success grade II of 61% (bone loss of ≤3 mm) were achieved. None of the evaluated baseline parameters affected bone loss. The survival rate of the zirconia implants was comparable to market-available titanium implants. However, an increased marginal bone loss was observed with a high peri-implantitis incidence and a resulting low implant success rate.

Reconstruction of dental roots for implant planning purposes: a feasibility study

Purpose

Modern virtual implant planning is a time-consuming procedure, requiring a careful assessment of prosthetic and anatomical factors within a three-dimensional dataset. In order to facilitate the planning process and provide additional information, this study examines a statistical shape model (SSM) to compute the course of dental roots based on a surface scan.

Material and methods

Plaster models of orthognathic patients were scanned and superimposed with three-dimensional data of a cone-beam computer tomography (CBCT). Based on the open-source software “R”, including the packages Morpho, mesheR, Rvcg and RvtkStatismo, an SSM was generated to estimate the tooth axes. The accuracy of the calculated tooth axes was determined using a leave-one-out cross-validation. The deviation of tooth axis prediction in terms of angle or horizontal shift is described with mean and standard deviation. The planning dataset of an implant surgery patient was additionally analyzed using the SSM.

Results

71 datasets were included in this study. The mean angle between the estimated tooth-axis and the actual tooth-axis was 7.5 ± 4.3° in the upper jaw and 6.7 ± 3.8° in the lower jaw. The horizontal deviation between the tooth axis and estimated axis was 1.3 ± 0.8 mm close to the cementoenamel junction, and 0.7 ± 0.5 mm in the apical third of the root. Results for models with one missing tooth did not differ significantly. In the clinical dataset, the SSM could give a reasonable aid for implant positioning.

Conclusions

With the presented SSM, the approximate course of dental roots can be predicted based on a surface scan. There was no difference in predicting the tooth axis of existent or missing teeth. In clinical context, the estimation of tooth axes of missing teeth could serve as a reference for implant positioning. However, a higher number of training data must be achieved to obtain increasing accuracy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11548-022-02716-x.

Impact of radiographic field-of-view volume on alignment accuracy during virtual implant planning: A noninterventional retrospective pilot study

OBJECTIVE

To evaluate the impact of reducing the radiographic field-of-view (FOV) on the trueness and precision of the alignment between cone beam computed tomography (CBCT) and intraoral scanning data for implant planning.

MATERIALS AND METHODS

Fifteen participants presenting with one of three clinical scenarios: single tooth loss (ST, n=5), multiple missing teeth (MT, n=5), and presence of radiographic artifacts (AR, n=5) were included. CBCT volumes covering the full arch (FA) were reduced to the quadrant (Q) or the adjacent tooth/teeth (A). Two operators, an expert (exp) in virtual implant planning and an inexperienced clinician, performed multiple superimpositions, with FA-exp serving as a reference. The deviations were calculated at the implant apex and shoulder levels. Thereafter, linear mixed models were adapted to investigate the influence of FOV on discrepancies.

RESULTS

Evaluation of trueness compared to FA-exp resulted in the largest mean (AR-A: 0.10 ± 0.33 mm) and single maximum discrepancy (AR-Q: 1.44 mm) in the presence of artifacts. Furthermore, for the ST group, the largest mean error (-0.06 ± 0.2 mm, shoulder) was calculated with the FA-FOV, while for MT, with the intermediate volume (-0.07 ± 0.24 mm, Q). In terms of precision, the mean SD intervals were ≤0.25 mm (A-exp). Precision was influenced by FOV volume (FA<Q<A) but not by operator expertise.

CONCLUSIONS

For single posterior missing teeth, an extended FOV does not improve registration accuracy. However, in the presence of artifacts or multiple missing posterior teeth, caution is recommended when reducing FOV.

In Vitro Time Efficiency, Fit, and Wear of Conventionally- versus Digitally-Fabricated Occlusal Splints

The purpose of the study was to compare conventional to digital workflows of occlusal splint production regarding time efficiency, overall fit, and wear. Fifteen Michigan splints were fabricated with a conventional and digital method. The duration for the dentist’s and the dental technician’s workload was recorded. Subsequently, the overall fit was examined with a four-level score (1–4). Paired t-tests were used to compare the time results for the conventional and digital workflows and the sign test to compare the overall fit. The mean time (16 min 58 s) for computerized optical impressions was longer than for conventional impressions (6 min 59 s; p = 0.0001). However, the dental technician needed significantly less mean time for the digital splint production (47 min 52 s) than for the conventional (163 min 32 s; p = 0.001). The overall fit of the digitally-fabricated splints was significantly better compared to the conventionally-fabricated splints (p = 0.002). There was no impact of the different materials used in the conventional and digital workflow on the wear (p = 0.26). The results suggest that the digital workflow for the production of occlusal splints is more time efficient and leads to a better fit than the conventional workflow.

Creating an anatomical wax-up in partially edentulous patients by means of a statistical shape model

PURPOSE

Creating wax-ups of missing teeth for backward-planning in implant surgery is a complex and time-consuming process. To facilitate implant-planning procedures, the automatic generation of a virtual wax-up would be useful. In this study, the reconstruction of missing teeth in partially edentulous patients was performed automatically using a newly developed software. The accuracy was investigated in order to test its clinical applicability.

MATERIAL AND METHODS

This study presents a new method for creating an automatic virtual wax-up, which could serve as a basic tool in modern implant planning procedures. First, a statistical shape model (SSM) based on 76 lower and upper arch scans from dentally healthy individuals was generated. Then artificially generated tooth gaps were reconstructed. The accuracy of the workflow was calculated using a Leave-One Out cross validation (LOOCV) and was given as median deviation (mm). Scans of three clinical cases with partial edentulism were equally reconstructed using the SSM and compared to the final prosthodontic work.

RESULTS

The reconstruction of the artificial tooth gaps could be performed with the following median reconstruction accuracy: gap 21 with 0.15mm; gap 27 with 0.20mm; gap 34 with 0.22mm: gap 36 with 0.22mm; gap 12-22 with 0.22mm; gap 34-36 with 0.22mm. A scenario for a close to edentulous lower jaw with all teeth missing except teeth 33 and 43 could be reconstructed with a median reconstruction accuracy of 0.37mm. The median tooth gap deviation of the SSM-based reconstruction in clinical cases differed from the final inserted prosthodontic teeth by 0.49mm-0.86mm in median.

CONCLUSION

A first feasibility of creating virtual wax-26 ups using a SSM could be shown. Artificially generated tooth gaps could be reconstructed close to original with the proposed workflow. In the clinical cases the SSM proposes an anatomical reconstruction, which does not yet consider prosthodontic aspects. To obtain clinical use contact to antagonist teeth must be considered and more training data must be implemented. However, the presented method offers a fast and viable way for the approximate placement of missing crowns. This could be used in a digital planning workflow when implant position must be determined.

Restoration of 1325 teeth with partial-coverage crowns manufactured from high noble metal alloys: a retrospective case series 18.8 years after prosthetic delivery

OBJECTIVES

To evaluate long-term survival and success rates of conventionally cemented partial-coverage crowns (PCCs) manufactured from high noble metal alloys (hn).

MATERIAL AND METHODS

Restoration-, periodontal- and tooth-related criteria on patients, restored with a single or multiple conventionally cemented hnPCCs in a private dental office were collected from existing patient records. With regard to semi-annual follow-ups, data of the most recent clinical evaluations were considered. Kaplan-Meier and log-rank tests were used for statistical analyses. Level of significance was set at p ≤ .05.

RESULTS

Between 09/1983 and 09/2009, 1325 hnPCCs were conventionally cemented on 1325 teeth in 266 patients (mean age: 44.5 ± 10.7 years). Due to various reasons, 81 hnPCCs showed complications, documenting a success rate of 93.9% after a mean observation period of 18.8 ± 5.7 years. Of these, additional 14 restorations were counted as survival, resulting in a survival rate of 94.9%. Most frequent complications were periodontal issues (n = 29, 35.8%). Significantly higher success rates were documented for hnPCCs of patients aged between 37 and 51 years (p = .012).

CONCLUSION

Partial-coverage crowns from high noble metal alloys showed excellent survival and success rates after a mean observation period of 18.8 ± 5.7 years. Higher patient age was one of the risk factors.

CLINICAL RELEVANCE

According to the results of this study, hnPCCs still represent an excellent therapeutic option-even in modern dentistry.

A Novel Zirconia-Based Composite Presents an Aging Resistant Material for Narrow-Diameter Ceramic Implants

A novel ceria-stabilized zirconia-alumina-aluminate composite (Ce-TZP-comp) that is not prone to aging presents a potential alternative to yttrium-stabilized zirconia for ceramic oral implants. The objective of this study was to evaluate the long-term stability of a one-piece narrow-diameter implant made of Ce-TZP-comp. Implant prototypes with a narrow (3.4 mm) and regular (4.0 mm) diameter were embedded according to ISO 14801, and subgroups (n = 8) were subsequently exposed to dynamic loading (10⁷ cycles, 98N) and/or hydrothermal treatment (aging, 85 °C). Loading/aging was only applied as a combined protocol for the 4.0 mm diameter implants. One subgroup of each diameter remained untreated. One sample was cross-sectioned from each subgroup and evaluated with a scanning electron microscope for phase-transformation of the lattice. Finally, the remaining samples were loaded to fracture. A multivariate linear regression model was applied for statistical analyses (significance at p < 0.05). All samples withstood the different loading/aging protocols and no transformation propagation was observed. The narrow diameter implants showed the lowest fracture load after combined loading/aging (628 ± 56 N; p < 0.01), whereas all other subgroups exhibited no significantly reduced fracture resistance (between 762 ± 62 and 806 ± 73 N; p > 0.05). Therefore, fracture load values of Ce-TZP-comp implants suggest a reliable intraoral clinical application in the anterior jaw regions.

Bond strength of conventional, subtractive, and additive manufactured denture bases to soft and hard relining materials

OBJECTIVE

To investigate the tensile and flexural strength of poured, subtractive, and additive manufactured denture base methacrylates bonded to soft and hard relining materials after hydrothermal cycling and microwave irradiation.

METHODS

This study included a conventional (CB), subtractive (SB), and additive (AB) base material as well as a soft (SCR) and hard (HCR) chairside and one hard laboratory-side (HLR) relining material. Reference bodies of the base materials and bonded specimens to the relining materials were produced with a rectangular cross-section. The specimens were either pre-treated by water storage (50 h, 37 °C), hydrothermal cycling (5000 cycles, 5 °C and 55 °C, 30 s each), or microwave irradiation (6 cycles, 640 W, 3 min, wet). A tensile and four-point bending test were performed for a total of 504 specimens. Data were analysed using multivariate analysis of variance (MANOVA) with post-hoc Tukey tests (α = 0.05).

RESULTS

In comparison with the other reference groups SB showed marginally higher tensile and flexural strength (p < 0.047). Bond strength to SCR was affected neither by the base material nor by the pre-treatment (p > 0.085). HCR demonstrated twice the bond strength to AB compared with SB and CB (p ≤ 0.001). HLR showed the highest bond strength to CB (p ≤ 0.001). There was no difference between the specimens after hydrothermally cycling and microwave irradiation (p > 0.318).

SIGNIFICANCE

The bond strength of hard relining materials to subtractive and additive manufactured denture bases differ compared with conventional pouring.

Retrospective long-term clinical evaluation of implant-prosthetic rehabilitations after head and neck cancer therapy

OBJECTIVE

To assess clinical and patient-reported outcomes of implant-prosthetic rehabilitations in patients with a history of head-neck cancer (HNC), treated with tumor resection without (TR) or with adjuvant radiotherapy (TR/RT). A healthy cohort rehabilitated with the same reconstructive protocols served as control group (C).

MATERIALS AND METHODS

A total of 28 women and 29 men were considered in the present retrospective study. Participants received 322 implants, finally supporting 79 prosthetic reconstructions. Primary outcome was the assessment of implant and prosthetic survival rates. Furthermore peri-implant soft tissue parameters (attached peri-implant mucosa, AM; modified bleeding and plaque indices, mBI/mPI; probing depth, PD) and prosthetic technical complications were documented. Patient-reported outcome measures (PROMs) by means of visual analog scales (VAS) and the Oral Health Impact Profile German 14 form (OHIP G14) were collected. For statistical purposes Chi-square and Mann-Whitney-U-Test were adapted.

RESULTS

After a mean follow-up of 81.2 ± 50.3 months, implant survival rate was 98.1% (HNC-TR), 98.2% (HNC-TR/RT) and 100.0% (C), respectively (four implants failed in the HNC groups). HNC-TR/RT showed significant higher mPI and mBI compared to C. Within HNC-TR/RT, vestibuloplasty significantly reduced mBI and PD values. No failures occurred at the prosthetic level. Overall, higher VAS scores were reported for bar- compared with Locator-retained prostheses. Furthermore, increased OHIP G14 values resulted for HNC-TR/RT.

CONCLUSIONS

High survival rates on implant and prosthetic level were observed. The use of soft tissue grafts resulted in stabilization of the peri-implant mucosa in irradiated patients. In terms of retention and chewing ability, participants preferred bars over Locator attachments.

Polymers for conventional, subtractive, and additive manufacturing of occlusal devices differ in hardness and flexural properties but not in wear resistance

OBJECTIVES

To investigate the wear resistance of polymers for injection molding, subtractive and additive manufacturing of occlusal devices in comparison with enamel antagonist wear and material properties (i.e., hardness, flexural strength, and flexural modulus).

METHODS

Injection molding was compared with milling and the additive technologies stereolithography, low force stereolithography, and digital light processing. For each material, eight specimens were produced for wear measurements. Extracted human premolars served as indenters. All samples were subjected to two series of a 2-body wear test consisting of 200,000 circular loading cycles with an applied load of 1) 20 N and 2) 50 N in a thermocycling environment (5/55 °C, 30 s, 3860 cycles, H₂O). Wear resistance was characterized by means of maximum depth and volume of the resulting traces. In addition, enamel wear of the indenters and Vickers hardness, flexural strength, and flexural modulus of the polymers were determined. Wear was statistically analyzed with linear general models for repeated measures and material properties with one-way ANOVA with post-hoc Tukey-HSD tests.

RESULTS

Wear of the antagonists was not influenced by the material (P ≥ 0.343). Likewise, no differences in wear resistance were found between materials after cyclic loading with 20 N or 50 N (P ≥ 0.074). Material properties investigated revealed decreased values for the resins for the additive manufacturing with the exception of flexural strength of one material.

SIGNIFICANCE

Within the limitations of this in-vitro study, arylates for conventional, subtractive, and additive manufacturing of occlusal devices differ in material properties but not in wear resistance and antagonist wear.

Accuracy and its impact on fit of injection molded, milled and additively manufactured occlusal splints

Occlusal devices to reduce symptoms of bruxism and temperomandibular disorders can nowadays be manufactured in a digital workflow but studies comparing the accuracy of those occlusal devices are still limited. Therefore, the aim of this investigation was to investigate the accuracy of injection molding compared with four computer-aided design (CAD) and computer-aided manufacturing (CAM) techniques for the manufacturing of occlusal devices. In addition, the number of contact points and retention were evaluated to assess clinical relevance. A conventional workflow consisting of alginate impression, wax-up, and injection molding (IM) and digital workflows including intraoral scanning, digital design, and subtractive manufacturing (SM) or additive manufacturing by using stereolithography (SLA), digital light processing (DLP), and material jetting (Polyjet) were investigated. Sixteen splints were fabricated with each method. The intaglio surfaces of the splints were laser scanned and superimposed with the reference data sets to analyze the surface deviations. In addition, the number of contact points after repositioning the splints on the reference model was evaluated with occlusal foil. Finally, the retention was measured in a tensile test. One-way ANOVA with post hoc Tukey tests were used for statistical analyses (α = .05). IM and SM splints demonstrated the highest manufacturing accuracy without significant differences to each other (P > .985). Additive manufactured splints revealed greater deviations with equal results for SLA and Polyjet (P > .949) and significantly higher deviations for DLP compared to all other groups (P < .002). Comparable retention force was measured for IM, SM, and SLA (P > .923), whereas Polyjet splints showed the greatest variability. IM and SM splints presented the most contact points (P = .505). Additive manufactured splints demonstrated fewer contacts without significant difference to each other (P > .116). It can be concluded, that there is no difference in manufacturing accuracy, retention, and number of contacts between IM and SM splints. AM splints demonstrated higher, however, clinically acceptable deviations.

How Accurate Is Oral Implant Installation Using Surgical Guides Printed from a Degradable and Steam-Sterilized Biopolymer?

3D printed surgical guides are used for prosthetically-driven oral implant placement. When manufacturing these guides, information regarding suitable printing techniques and materials as well as the necessity for additional, non-printed stock parts such as metal sleeves is scarce. The aim of the investigation was to determine the accuracy of a surgical workflow for oral implant placement using guides manufactured by means of fused deposition modeling (FDM) from a biodegradable and sterilizable biopolymer filament. Furthermore, the potential benefit of metal sleeve inserts should be assessed. A surgical guide was designed for the installation of two implants in the region of the second premolar (SP) and second molar (SM) in a mandibular typodont model. For two additive manufacturing techniques (stereolithography [SLA]: reference group, FDM: observational group) n = 10 surgical guides, with (S) and without (NS) metal sleeves, were used. This resulted in 4 groups of 10 samples each (SLA-S/NS, FDM-S/NS). Target and real implant positions were superimposed and compared using a dedicated software. Sagittal, transversal, and vertical discrepancies at the level of the implant shoulder, apex and regarding the main axis were determined. MANOVA with posthoc Tukey tests were performed for statistical analyses. Placed implants showed sagittal and transversal discrepancies of <1 mm, vertical discrepancies of <0.6 mm, and axial deviations of ≤3°. In the vertical dimension, no differences between the four groups were measured (p ≤ 0.054). In the sagittal dimension, SLA groups showed decreased deviations in the implant shoulder region compared to FDM (p ≤ 0.033), whereas no differences in the transversal dimension between the groups were measured (p ≤ 0.054). The use of metal sleeves did not affect axial, vertical, and sagittal accuracy, but resulted in increased transversal deviations (p = 0.001). Regarding accuracy, biopolymer-based surgical guides manufactured by means of FDM present similar accuracy than SLA. Cytotoxicity tests are necessary to confirm their biocompatibility in the oral environment.

3-D Printed Protective Equipment during COVID-19 Pandemic

While the number of coronavirus cases from 2019 continues to grow, hospitals are reporting shortages of personal protective equipment (PPE) for frontline healthcare workers. Furthermore, PPE for the eyes and mouth, such as face shields, allow for additional protection when working with aerosols. 3-D printing enables the easy and rapid production of lightweight plastic frameworks based on open-source data. The practicality and clinical suitability of four face shields printed using a fused deposition modeling printer were examined. The weight, printing time, and required tools for assembly were evaluated. To assess the clinical suitability, each face shield was worn for one hour by 10 clinicians and rated using a visual analogue scale. The filament weight (21-42 g) and printing time (1:40-3:17 h) differed significantly between the four frames. Likewise, the fit, wearing comfort, space for additional PPE, and protection varied between the designs. For clinical suitability, a chosen design should allow sufficient space for goggles and N95 respirators as well as maximum coverage of the facial area. Consequently, two datasets are recommended. For the final selection of the ideal dataset to be used for printing, scalability and economic efficiency need to be carefully balanced with an acceptable degree of protection.

Fracture Resistance of Zirconia Oral Implants In Vitro: A Systematic Review and Meta-Analysis

Various protocols are available to preclinically assess the fracture resistance of zirconia oral implants. The objective of the present review was to determine the impact of different treatments (dynamic loading, hydrothermal aging) and implant features (e.g., material, design or manufacturing) on the fracture resistance of zirconia implants. An electronic screening of two databases (MEDLINE/Pubmed, Embase) was performed. Investigations including > 5 screw-shaped implants providing information to calculate the bending moment at the time point of static loading to fracture were considered. Data was extracted and meta-analyses were conducted using multilevel mixed-effects generalized linear models (GLMs). The Šidák method was used to correct for multiple testing. The initial search resulted in 1864 articles, and finally 19 investigations loading 731 zirconia implants to fracture were analyzed. In general, fracture resistance was affected by the implant design (1-piece > 2-piece, p = 0.004), material (alumina-toughened zirconia/ATZ > yttria-stabilized tetragonal zirconia polycrystal/Y-TZP, p = 0.002) and abutment preparation (untouched > modified/grinded, p < 0.001). In case of 2-piece implants, the amount of dynamic loading cycles prior to static loading (p < 0.001) or anatomical crown supply (p < 0.001) negatively affected the outcome. No impact was found for hydrothermal aging. Heterogeneous findings of the present review highlight the importance of thoroughly and individually evaluating the fracture resistance of every zirconia implant system prior to market release.

Guided implant surgery for one-piece ceramic implants: a digital workflow

BACKGROUND

Accurate implant placement in the bone is key to successful implant treatment. Once inserted, it can be difficult to correct the orientation of the implant axis, especially of a one-piece implant. Prosthetic-driven digital implant planning in combination with fully guided implant surgery can offer additional safety in such cases.

CASE PRESENTATION

The patient presented with a wide, edentulous interdental space extending from sites 13 to 16, which was to be restored with three one-piece zirconia implants supporting a zirconia fixed partial denture comprizing a cantilever to the mesial aspect. Digital planning based on DICOM (Digital Imaging and Communications in Medicine) and intraoral surface data was performed to ensure optimal positioning. Guided implant placement was executed using a contra-angle handpiece with special attachments and a compatible, sleeveless drill guide. Impressions of the implants for the final restoration were acquired using an intraoral scanner. Reflection-related errors were compensated for by using the given digital abutment geometry. The DICOM and STL datasets were superimposed and used as the basis for fabricating a monolithic zirconia restoration through a subtractive milling process. The final restoration was adhesively cemented.

CONCLUSIONS

By using a prosthetic-driven implant planning strategy, it was possible to place the one-piece ceramic implants without an available implant manufacturer's guide-based solution. This was accomplished using a contra-angle surgical handpiece with special attachments and a compatible drill guide. This approach is particularly recommended for the placement of one-piece implants, which otherwise require irreversible abutment grinding for the adjustment of the implant axis orientation after placement. To increase the precision of the digital impressions of the implants, the ideal abutment geometry was imported and superimposed onto the scan data. The results demonstrate that the proposed method can dispense with the need for gingival retraction when acquiring impressions for implants of this type in the future.

Digital and Orthodontically Driven Implant Planning: A Multidisciplinary Case History Report

Patients presenting both severe maxillary atrophy and dental malposition require a multidisciplinary treatment approach to achieve optimal esthetic and functional results. This case history report demonstrates how digital treatment planning and teeth set-up can serve as a reference for surgical, orthodontic, and prosthodontic procedures, leading to an all-ceramic full-arch implant-supported fixed prosthesis.

Survival rates and complication behaviour of tooth implant-supported, fixed dental prostheses: A systematic review and meta-analysis

OBJECTIVE

To assess the survival and complication rates of tooth-implant supported fixed dental prostheses (T-I FDPs).

SOURCES

An electronic search in MEDLINE/PubMed, Cochrane Library, and Embase was conducted using MeSH terms to identify randomised controlled trials (RCTs) or prospective studies with an observation period of at least 3 years, including at least 10 participants.

STUDY SELECTION

Included studies were qualitatively assessed. Survival rates of T-I FDPs and implants as well as technical and biological complications were obtained. Failure and complication rates were pooled by weighting each rate in inverse proportion to its variance.

DATA

A total of eight studies were considered for qualitative analysis; seven studies with a minimum follow-up of five years were included for quantitative analysis. Estimated survival rates of T-I FDPs were 90.8% (95% CI: 86.4-93.8%) after five years and 82.5% (95% CI: 74.7-88.0%) after 10 years. Implant survival estimates were 94.8% (90.9-97.0%) and 89.8% (82.7-99.4%) after 5 and 10 years, respectively. From a total of 185 T-I FDPs, 21 (11.4%) minor and 23 (12.4%) major biological complications were observed, whereas 23 (12.4%) minor and three (1.6%) major technical complications occurred.

CONCLUSIONS

Due to the lack of well-designed studies exceeding a 10-year follow-up, prognosis for the long -term can hardly be given. Considering the inclusion criteria of this systematic review, T-I FDP-supported fixed dental prostheses show acceptable survival rates after five and 10 years. Rigidly constructed T-I FDPs should be preferred. With regard to the available data, these conclusions are valid only for three- to four-unit T-I FDPs.

CLINICAL SIGNIFICANCE

Tooth-implant supported fixed dental prostheses are a recommendable treatment option in partial dentition. Based on the current literature, they should be rigidly constructed with a maximum number of four units.

Clinical outcomes of partial and full-arch all-ceramic implant-supported fixed dental prostheses. A systematic review and meta-analysis

OBJECTIVE

To assess the survival and technical complication rate of partial and full-arch all-ceramic implant-supported fixed dental prostheses (P-FDP/FA-FDP) and supporting implants.

MATERIALS AND METHODS

An electronic search through three databases (MEDLINE/Pubmed, Cochrane Library, Embase) was conducted to identify relevant clinical studies with an observation period of at least 12 months, including ≥15 patients. Reconstruction and implant survival rates, technical complications and confounding variables such as processed/installed materials, retention mode and location in the mouth were obtained. Failure and complication rates were analyzed using standard Poisson regression models to calculate 5-year survival and complication estimates.

RESULTS

A total of five studies for the P-FDP group and seven studies for the FA-FDP group were included, throughout evaluating veneered zirconia reconstructions. In the P-FDP group, reconstructions were located in posterior regions. Meta-analysis indicated survival estimates on the reconstruction level of 98.3% and 97.7% for P- and FA-FDPs after 5 years. However, chipping of the veneering ceramic was frequent, resulting in estimated 5-year complication rates of 22.8% (P-FDPs) and 34.8% (FA-FDPs). Five-year survival estimates of implants supporting P-FDPs and FA-FDPs of 98.5% and 99.4% were calculated, respectively. Including a total of 540 FDPs, one screw-loosening and 11 de-cementations were reported. Confounding variables were not found to have a significant influence on survival and complication rates.

CONCLUSIONS

All-ceramic implant-supported P- and FA-FDPs comprising veneered zirconia frameworks showed high survival but clinically inacceptable fracture rates of the veneering ceramic. Their suitability with regard to this indication and a successful long-term outcome needs to be further evaluated.

The clinical performance of all-ceramic implant-supported single crowns: A systematic review and meta-analysis

OBJECTIVE

This review aimed at evaluating the survival and technical complication rates of all-ceramic implant-supported single crowns (SC).

MATERIAL AND METHODS

Three electronic databases were searched for clinical studies conducted at ≥ 15 patients examining implant-supported all-ceramic SCs over ≥ 12 months. Survival rates of implants and restorations plus technical complication rates of SCs were calculated and tested for statistical correlation with confounding variables. Statistical analysis was performed using a negative binomial distribution model to calculate 5- and 10-year survival and complication estimates.

RESULTS

Forty-one included studies reported on implant-supported SCs made of veneered and monolithic high-strength oxide ceramics, monolithic, and veneered glass-based ceramics and of a monolithic resin-nano-ceramic (RNC). Survival estimates for SCs of 93% (95% CI: 86.6%-96.4%) after 5 years and 94.4% (95% CI: 91.1%-96.5%) after 10 years were calculated, corresponding values for implant survival were 95.3% (95% CI: 90.6%-97.7%) and 96.2% (95% CI: 95.1%-97.1%). Technical complication rates after 5/10 years were as follows: chipping 9.0% (95% CI: 5.4%-14.8%)/2.7% (95% CI: 2.1%-3.5%), framework fractures 1.9% (95% CI: 0.7%-4.9%)/1.2% (95% CI: 1%-1.5%), screw loosening 3.6% (95% CI: 1.6%-8.4%)/5.2% (95% CI: 3.6%-7.5%), and decementations with 1.1% (95% CI: 0.4%-2.8%) after 5 years. Some confounding variables influenced the above-mentioned estimates significantly.

CONCLUSIONS

All-ceramic implant-supported SCs showed-with the exception of a RNC material-high survival rates. However, failures and technical complications occurred which have to be considered when informing patients on the treatment with implant-supported all-ceramic SCs.

Osseointegration of zirconia dental implants in animal investigations: A systematic review and meta-analysis

OBJECTIVE

To determine the osseointegration rate of zirconium dioxide (ZrO₂) dental implants in preclinical investigations.

DATA

Data on the osseointegration rate was extracted considering the bone to implant contact (BIC), removal torque analysis (RTQ) and push-in tests. Meta analyses were conducted using multilevel multivariable mixed-effects linear regression models. The Šidák method was used in case of multiple testing.

SOURCES

An electronic screening of the literature (MEDLINE/Pubmed, Cochrane Library and Embase) and a supplementary manual search were performed. Animal investigations with a minimum sample size of 3 units evaluating implants made of zirconia (ZrO₂) or its composites (ZrO₂>50vol.%) were included.

STUDY SELECTION

The search provided 4577 articles, and finally 54 investigations were included and analyzed. Fifty-two studies included implants made from zirconia, 4 zirconia composite implants and 37 titanium implants. In total, 3435 implants were installed in 954 animals.

CONCLUSIONS

No significant influence of the evaluated bulk materials on the outcomes of interest could be detected. When comparing different animal models, significant differences for the evaluated variables could be found. These results might be of interest for the design of further animal investigations.

Clinical and patient-reported outcomes of zirconia-based implant fixed dental prostheses: Results of a prospective case series 5 years after implant placement

OBJECTIVE

To evaluate the clinical and patient-reported outcome of all-ceramic zirconia implant supported fixed dental prostheses (FDPs) 5 years after implant installation.

MATERIALS AND METHODS

Thirteen patients were treated with two terminally placed one-piece zirconia implants for a three-unit FDP each. The FDPs consisted of a CAD/CAM-fabricated zirconia framework over-pressed with a fluor-apatite veneering ceramic and were adhesively cemented. Survival and success were assessed by applying modified US Public Health Service (USPHS) criteria and preparation of Kaplan-Meier (KM) plots. Alpha and Bravo ratings were accepted for success (among others including small area veneer chippings and occlusal roughness), whereas Charlie ratings allowing for intra-oral correction (e.g., polishing) were accepted for survival. Furthermore, patient-reported outcome measures (PROMs) were analyzed with the help of visual analogue scales (VAS). Wilcoxon matched-pairs signed-rank test (USPHS criteria) and linear mixed models (PROMs) were used to evaluate time effects on response variables.

RESULTS

All patients were available 61.8 ± 1.1 months after implant installation (53.6 ± 3.1 months after final prosthesis insertion). FDP survival was 100%. Significant incidence of veneer chipping (p = .0096) and occlusal roughness (p = .0019) was observed. Charlie rated extent of both phenomena resulted in a KM success estimate of 38.5% (95% CI: 14.1%-62.8%; seven FDPs with obvious roughness, three of them with extended veneer chipping). Compared with the pre-treatment assessments (30%-81% of satisfaction), all surveys at prosthetic delivery showed significantly improved VAS scores (66%-93%; p ≤ .038), except for speech (p = .341). Concerning function, esthetics and self-esteem, no decrease in satisfaction could be observed until the end of follow-up (90%-96%; p ≥ .057), whereas perception of sense (92%) and speech (95%) increased over time (p ≤ .030). Occurrence of technical complications did not correlate with patient satisfaction.

CONCLUSIONS

Bi-layered FDPs made from zirconia/fluor-apatite highly satisfied patients but showed significant incidence of technical complications.

Implant-retained prostheses: ball vs. conus attachments - A randomized controlled clinical trial

OBJECTIVE

To evaluate implant survival, peri-implant tissue conditions, prosthodontic maintenance requirements and patient satisfaction of two differently retained implant-supported mandibular overdentures (IOD) after the 3 years of observation.

MATERIALS AND METHODS

Twenty-five patients with edentulous mandibles received two implants each. Twelve patients were randomly selected to receive ball attachments, whereas 13 patients received prefabricated coni. Implant survival, peri-implant parameters (modified Plaque Index, Bleeding on Probing, modified Gingival Index, probing depth and marginal bone loss) and patient satisfaction were assessed. Additionally, prosthodontic maintenance was monitored. Clinical and radiographic follow-ups were performed 1, 2 and 3 years after prosthetic delivery. The Kaplan-Meier method was used to calculate complication rates.

RESULTS

After a mean observation period of 29.6 months, an implant survival rate of 100% could be observed. There were no significant differences in the peri-implant parameters. During the observation period, six patients with conus attachment refused to further participate in follow-ups due to dissatisfaction with their treatment and had to be regarded as dropouts. Based on the Kaplan-Meier method, inacceptable retention was calculated for 80% and 75% of the patients in the ball and the conus groups, respectively. Patient satisfaction was 64% for the ball- and 100% for the conus-retained IODs, the latter only respecting five of initially 13 patients.

CONCLUSION

The evaluated treatment method revealed high implant survival rates, but the prosthetic reconstruction required intensive maintenance. Therefore, a trend toward the reduced patient satisfaction was observed, and the promoted economy of the evaluated attachment systems should be questioned. For the conical attachment, the recommendation of the manufacturer is to use four interforaminal implants to support a removable prostheses.

All-Ceramic Single Crown Restauration of Zirconia Oral Implants and Its Influence on Fracture Resistance: An Investigation in the Artificial Mouth

The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without crowns (N, 24 samples) were subdivided according to the loading protocol, resulting in three groups of 8 samples each: Group “0” was not exposed to cyclic loading, whereas groups “5” and “10” were loaded with 5 and 10 million chewing cycles, respectively. This resulted in 6 different groups: C0/N0, C5/N5 and C10/N10. Subsequently, all 48 implants were statically loaded to fracture and bending moments were calculated. All implants survived the artificial aging. For the static loading the following average bending moments were calculated: C0: 326 Ncm; C5: 339 Ncm; C10: 369 Ncm; N0: 339 Ncm; N5: 398 Ncm and N10: 355 Ncm. To a certain extent, thermomechanical cycling resulted in an increase of fracture resistance which did not prove to be statistically significant. Regarding its fracture resistance, the evaluated ceramic implant system made of Y-TZP seems to be able to resist physiological chewing forces long-term. Restauration with all-ceramic single crowns showed no negative influence on fracture resistance.