Strength and stiffness of interim materials and interim fixed dental prostheses when tested at different loading rates.

STATEMENT OF PROBLEM: How the loading rate might affect the mechanical properties of interim materials and interim fixed dental prostheses is unclear. PURPOSE: The purpose of this in vitro study was to compare the material stiffness, material strength, and structural strength of interim 3-unit fixed dental prostheses fabricated from 3 interim materials when stressed at different loading rates. MATERIAL AND METHODS: Bar-shaped specimens and anatomically correct interim 3-unit fixed dental prostheses with a modified-ridge lap pontic were fabricated from polyethyl methacrylate resin (Trim) and 2 bis-acrylic composite resins (TempSmart; Integrity) (n=10). Flexural modulus and strength of the bar specimens, representing material stiffness and strength, were determined with a 4-point bend test in a universal testing machine. The structural strength of the prosthesis was assessed from the failure load from a vertical force applied on the occlusal surface of the pontic. Three loading rates, 0.5, 5, or 10 mm/min, were evaluated. Results were statistically analyzed with 2-way analysis of variance and multiple comparisons (α=.05). RESULTS: Loading rate and material significantly affected flexural modulus, flexural strength, and structural strength (P<.05). Increasing loading rate significantly increased the flexural modulus of all materials (P<.05), but the effect of loading rate on the flexural strength of bis-acrylic composite resins was mostly insignificant. Polyethyl methacrylate specimens did not fracture when loaded at 0.5 or 5 mm/min, and the interim fixed dental prostheses made from polyethyl methacrylate did not fracture at the 0.5 mm/min loading rate. Dual-polymerizing bis-acrylic composite resin had significantly higher flexural modulus and strengths than autopolymerizing bis-acrylic composite resin. CONCLUSIONS: Polyethyl methacrylate resin had the lowest stiffness among the interim materials tested and did not fracture but excessively deformed at the low loading rate. Dual-polymerizing bis-acrylic composite resin consistently had higher stiffness and material strength and provided higher structural strength than the autopolymerizing bis-acrylic composite resin. Loading rate significantly affected the mechanical properties of polyethyl methacrylate resin (P<.05), but the effect was indistinct for the bis-acrylic materials.

Failure load of milled, 3D-printed, and conventional chairside-dispensed interim 3-unit fixed dental prostheses.

STATEMENT OF PROBLEM: New techniques and materials for the laboratory fabrication of interim fixed dental prostheses have gained in popularity, yet how their failure strengths compare with conventional chairside materials is unclear. PURPOSE: The purpose of this in vitro study was to compare the strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled polymethylmethacrylate (PMMA) or 3-dimensionally (3D) printed bis-acryl interim fixed dental prostheses with a traditional chairside-dispensed autopolymerizing bis-acryl prosthesis while taking into account the effect of loading rate and storage time. MATERIAL AND METHODS: A dentiform mandibular second premolar and second molar with a first molar pontic were prepared and scanned. Three groups of 3-unit interim fixed dental prostheses were fabricated: milled PMMA, 3D-printed bis-acryl, and chairside-dispensed autopolymerizing bis-acryl. The interim prostheses were evaluated for fit with a silicone disclosing material and cemented onto 3D-printed resin dies. The specimens were stored in 100% humidity at 37 °C. After 1 or 30 days of storage, the cemented interim prostheses were loaded to failure in a universal testing machine at 1 or 10 mm/min (n=15/group). Failure loads were analyzed by 3-way analysis of variance and multiple comparisons (α=.05). RESULTS: Mean ±standard deviation failure loads ranged from 363 ±93 N (3D-printed bis-acryl, 30 days, 1 mm/min) to 729 ±113 N (milled PMMA, 24 hours, 1 mm/min). Loading rate did not significantly affect failure load of the interim prostheses (P=.306). After 30 days of storage in 100% humidity, the failure load of milled PMMA and 3D-printed bis-acryl interim prostheses decreased significantly, but the chairside autopolymerizing bis-acryl prostheses were not affected. After 30 days of storage, the failure loads of milled PMMA and chairside autopolymerizing bis-acryl were not significantly different. CONCLUSIONS: Regardless of loading rate, interim fixed dental prostheses from milled PMMA had the highest initial strength 1 day after storage. Thirty days of exposure to humidity, however, reduced the strength of the CAD-CAM-manufactured interim prostheses, whereas the traditional chairside prostheses retained their strength.

Accuracy of Additively Manufactured and Milled Interim 3-Unit Fixed Dental Prostheses.

PURPOSE: To investigate the accuracy of additive manufacturing (AM) by means of internal fit of fixed dental prostheses (FDPs) fabricated with two AM technologies using different resins and printing modes (validated vs nonvalidated) compared to milling and direct manual methods. MATERIAL AND METHODS: Sixty 3-unit interim FDPs replacing the first mandibular molar were divided into 6 groups (n = 10): manual (Protemp 4), milled (Telio-CAD), and AM groups were subdivided based on AM technology (direct light processing (Rapidshape P30 [RS]) and stereolithography (FormLabs 2 [FL])) and the polymer type (P-Pro-C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, FL-Sh). Validated (RS-Sh and RS-St) or nonvalidated (FL-St and FL-Sh) modes were adopted for AM. The specimens were scanned to 3D align (GOM inspect) according to the triple scan method. The internal space between the FDPs and preparation surfaces in four sites (marginal, axial, occlusal, and total) was measured using equidistant surface points (GOM Inspect). Statistical analysis was done using Kruskal Wallis and Dunn post-hoc tests. (α = 0.05). RESULTS: One AM group (FL-Sh) and milling exhibited better adaptation compared to manual and RS-St at molar site (p < 0.05). FDPs with St resin (FL-St and RS-St) displayed bigger marginal space than milled, FL-Sh, and RS-Sh. The nonvalidated printing mode showed better mean space results (p < 0.05) with higher predictability and repeatability (p < 0.001). CONCLUSIONS: The AM interim FDPs tested provided valid alternatives to the milled ones in regard to their accuracy results. The printing mode, resin, and the AM technology used significantly influenced the manufacturing accuracy of interim FDPs, particularly at the marginal area. The nonvalidated printing mode with lower-cost 3D printers is a promising solution for clinical applications.

The effect of surface treatments on the color stability of CAD-CAM interim fixed dental prostheses.

STATEMENT OF PROBLEM: Additive manufacturing or 3D printing is gaining popularity in dentistry, including for interim fixed dental prostheses (IFDPs). However, evidence regarding the color stability of 3D-printed IFDPs is lacking. PURPOSE: The purpose of this in vitro study was to investigate whether different surface treatments could affect the color stability of milled and 3D-printed IFDPs after simulated physiological aging. MATERIAL AND METHODS: Forty milled IFDPs were fabricated with a 5-axis dental mill (DWX-51D; Roland DGA Corp) from polymethyl methacrylate disks (Temp Esthetic 98, A3.5, 98.5×16 mm; Harvest Dental Products, LLC). Forty 3D-printed IFDPs were fabricated with an in-office digital light processing 3D printer (MAX; Asiga) and light-polymerizing resin (NextDent Crown & Bridge A3.5; NextDent B.V). All milled and 3D-printed IFDPs were allocated into 4 different groups (n=10), according to different surface treatments: Control, Polish, Optiglaze, and Skinglaze. In the Control group, no surface treatment was applied to the IFDPs. For the Polish group, IFDPs were finished and polished with aluminum oxide finishers/polishers (Enhance PoGo Complete Kit; Dentsply Sirona). For the Optiglaze and Skinglaze groups, specimens were first finished and polished and prepared with additional light-polymerizing protective coatings (Optiglaze; GC America Inc, or New Outline Skin Glaze; anaxdent North America). Shade measurements were recorded with a digital spectrophotometer (Vita Easyshade V; VITA North America) before and after the thermocycling for the color stability comparisons. The effects of interim prosthesis type and surface treatments on ΔE∗, ΔL∗, Δa∗, and Δb∗ were examined using 2-way analysis of variance (ANOVA), and ΔE∗ was considered as the primary outcome variable. Post hoc pairwise comparisons were performed by using the Tukey honestly significant difference (HSD) method (α=.05 for all tests). RESULTS: Milled IFDPs had significantly smaller ΔE∗ than 3D-printed prostheses for the Control group only (P<.001). Within the milled IFDPs, Optiglaze group (mean ±standard deviation, 1.01 ±0.38) had significantly lower ΔE∗ than all the other surface treatments groups (Control group: 2.38 ±0.44, P<.001; Polish group: 1.83 ±0.51, P=.025; and Skinglaze group: 1.85 ±0.78, P=.021). Within the 3D-printed IFDPs, the Control group (3.83 ±0.71) had significantly larger ΔE∗ than all other surface treatments (Polish group: 2.66 ±0.89, P=.018; Skinglaze group: 1.40 ±0.73, P<.001; and Optiglaze group: 1.37 ±0.67, P<.001). The Polish group had significantly higher ΔE∗ than Skinglaze group (P=.009) and Optiglaze group (P=.007), while Skinglaze and Optiglaze groups were not significantly different from each other (P=1.000). CONCLUSIONS: For the milled IFDPs, only the nano-filled, light-polymerizing protective coating significantly lowered color changes after thermocycling simulating 6 months of intraoral physiological aging. For the 3D-printed IFDPs, surface polishing and both light-polymerizing protective coating agents all significantly reduced color changes of the prostheses after thermocycling. The protective effect of light-polymerizing coating agents was more substantial.

Staged extractions and implant placement in a periodontally compromised patient: A clinical report.

Staging the extraction of selected teeth in a periodontally compromised patient during complete mouth rehabilitation has advantages, including avoiding a transitional complete denture, keeping the patient with a fixed prosthesis throughout the treatment without the need to immediately load the implants, maintaining the interdental papillae, and providing comfort for the patient. The need for a multistep extended treatment and additional cost are the main disadvantage of this approach. This clinical report describes the clinical steps and follow-up of a staging approach and implant placement in a periodontally compromised patient with excessive gingival display to achieve a good functional and esthetic result.

Precise Reproduction of Soft Tissue Structure around the Pontic Area Using Computer-Aided Design and Manufacturing.

Reproducing soft tissue contours around a pontic area is important for the fabrication of an esthetic prosthesis, especially in the anterior area. A gingival model that precisely replicates the soft tissue structure around the pontic area can be easily obtained by taking a pick-up impression of an interim fixed dental prosthesis. After a working cast is fabricated using the customary technique, the pick-up model is superimposed onto the working model for the pontic area using computer-aided design and manufacturing (CAD/CAM). A definitive restoration using this technique would be well adapted to the pontic base, which is formed by the interim prosthesis.

Fabrication of an interim complete removable dental prosthesis with an in-office digital light processing three-dimensional printer: A proof-of-concept technique.

This report describes a proof of concept for fabricating an interim complete removable dental prosthesis with a digital light processing 3-dimensional (3D) printer. Although an in-office 3D printer can reduce the overall production cost for an interim complete removable dental prosthesis, the process has not been validated with clinical studies. This report provided a preliminary proof of concept in developing a digital workflow for the in-office additively manufactured interim complete removable dental prosthesis.

NON-REMOVABLE DENTURE PROTOTYPES, EFFECTIVE IN DENTAL IMPLANTATION.

Temporary prosthesis transformed into a prosthetic prototypes and manufactured by CAD/CAM technologies (computer copy milling) are used to specify the final form of future permanent restoration and to correct occlusal relationships, vertical size of non-removable dentures, and their occlusal surfaces. A progressive loading on bone tissue in the implantation area and soft tissues formation, have been assessed. In this regard, the choice and placement of temporary mini-implants, as the supports for non-removable denture prototypes for the period of osseointegration of two-stage intraosseous dental implants, are the issues of great importance. Temporary dental implants are the object of complex loads of different magnitude, duration and direction. The action of the prosthesis is closely related to load delivery to the surface of dental implant between the components of the system - "implant-temporary prosthesis". According to the study results, minimization of the momentum acting on temporary implants in the mesiodistal direction allows reducing stress level in the areas of permanent implant placement.

Use of a CAD-CAM poly(methyl methacrylate) interim prosthesis for direct intraoral splinting.

This article describes a technique where an interim computer-aided design and computer-aided manufacturing (CAD-CAM) prosthesis is milled from a poly(methyl methacrylate) blank to confirm esthetics, occlusion, function, phonetics, and accessibility for oral hygiene. The interim prosthesis is then sectioned and reconnected intraorally with autopolymerizing acrylic resin. This interim prosthesis is used to fabricate the definitive stone cast. The interim prosthesis is then scanned with a laboratory scanner. By applying this technique, the implant positioning can be related to the occlusal plane, the contours of the teeth, and the flange. The clinician can more effectively design the definitive prosthesis because the location of the implants and the exact contours of the teeth are all captured in a single digital file.

Creation of a 3-dimensional virtual dental patient for computer-guided surgery and CAD-CAM interim complete removable and fixed dental prostheses: A clinical report.

This clinical report proposes a digital workflow using 2-dimensional (2D) digital photographs, a 3D extraoral facial scan, and cone beam computed tomography (CBCT) volumetric data to create a 3D virtual patient with craniofacial hard tissue, remaining dentition (including surrounding intraoral soft tissue), and the realistic appearance of facial soft tissue at an exaggerated smile under static conditions. The 3D virtual patient was used to assist the virtual diagnostic tooth arrangement process, providing patient with a pleasing preoperative virtual smile design that harmonized with facial features. The 3D virtual patient was also used to gain patient's pretreatment approval (as a communication tool), design a prosthetically driven surgical plan for computer-guided implant surgery, and fabricate the computer-aided design and computer-aided manufacturing (CAD-CAM) interim prostheses.

Interim Prosthesis Options for Dental Implants.

Dental implants have become a popular treatment modality for replacing missing teeth. In this regard, the importance of restoring patients with function during the implant healing period has grown in recent decades. Esthetic concerns, especially in the anterior region of the maxilla, should also be considered until the definitive restoration is delivered. Another indication for such restorations is maintenance of the space required for esthetic and functional definitive restorations in cases where the implant site is surrounded by natural teeth. Numerous articles have described different types of interim prostheses and their fabrication techniques. This article aims to briefly discuss all types of implant-related interim prostheses by different classification including provisional timing (before implant placement, after implant placement in unloading and loading periods), materials, and techniques used for making the restorations, the type of interim prosthesis retention, and definitive restoration. Furthermore, the abutment torque for such restorations and methods for transferring the soft tissue from interim to definitive prostheses are addressed.

Using a Visible Light-Polymerized Resin to Fabricate an Interim Partial Removable Dental Prosthesis.

An interim partial removable dental prosthesis (RDP) is any dental prosthesis that replaces some teeth in a partially dentate arch designed to enhance esthetics, stabilization, and/or function for a limited period of time, after which it is to be replaced by a definitive dental prosthesis. This article describes a technique that uses a visible light-polymerized (VLP) resin as the base material for an interim partial RDP. This technique can be easily accomplished in a dental office or laboratory and results in a predictable dental prosthesis. This technique eliminates the need for laboratory processing.

Backside Wear Is Not Dependent on the Acetabular Socket Design in Crosslinked Polyethylene Liners.

BACKGROUND: Although it is understood that backside damage occurs in polyethylene acetabular liners, the effect of highly crosslinked polyethylene, which has completely replaced conventional polyethylene, has yet to be examined. QUESTIONS/PURPOSES: The purpose of this study was to answer the following questions: (1) With conventional polyethylene (CPE), did the acetabular design make a difference in backside wear? (2) Is there a difference in backside damage between CPE and crosslinked polyethylene (XLPE) liners? (3) With XLPE, is the difference in backside wear between designs still present? (4) Is there any difference in backside damage in various zones on backside of individual liners? METHODS: This single-institution retrieval analysis involved visual damage scoring on the backside of 233 polyethylene liners implanted between 2002 and 2011. The liners were retrieved from either polished/dovetail cups (PD) or roughened/wire cups (RW) made by two different manufacturers. The inserts were divided into four groups: PD-CPE (n = 105), PD-XLPE (n = 16), RW-CPE (n = 99), and RW-XLPE (n = 13). Aseptic loosening and polyethylene wear were the predominant reasons for revision of CPE liners, whereas instability and infection were the common reasons for revision of XLPE liners. The time in situ (TIS) was shorter for the XLPE liners as compared with the CPE liners (PD-CPE: 8.5 years [SD 4.4]; RD-CPE: 9.5 [SD 4.8]; PD-CPE: 3.8 [SD 3.7]; RD-XLPE: 4.0 [SD 4.3]). The backside of each liner was divided into five zones and graded initially from a scale of 0 to 3 for seven different damage modes by one observer. There was substantial interobserver (kappa 0.769) and intraobserver (0.736) reliability on repeat scoring. To compare the effects of crosslinking, a subset of the conventional polyethylene liners was matched to the crosslinked liners based on TIS, resulting in 16 per group for the two PD types and 13 per group for the two RW types. RESULTS: Total damage scores in the RW-CPE (19 ± 7) group were greater (p < 0.001) than the PD-CPE group (8 ± 4). Damage was reduced with XLPE (p = 0.02) only for the RW-XLPE (9 ± 9) versus RW-CPE-type sockets (4 ± 4). There was no difference (p = 0.16) between the RW-XLPE group and the PD-XLPE group. Damage scores in the peripheral zone of the locking mechanisms were higher for RW-CPE (4 ± 3) compared with PD-CPE (1.4 ± 1.0, p < 0.001) and RW-XLPE (1.3 ± 1.3, p = 0.02). Damage was greater (p < 0.001) within the superior zones (7 ± 4) compared with the inferior zones (3.0 ± 2.8) of all liners. CONCLUSIONS: The current study shows greater backside damage for CPE in the roughened, wire lock cups. XLPE was shown to be more resistant to backside damage for both socket designs. CLINICAL RELEVANCE: Although the polished/dovetail cups seem to cause less backside damage in the CPE liners than roughened/wire cups, the use of XLPE liners has been shown to protect the liner from backside damage in either cup design. If an acetabular shell has a functional locking mechanism, surgeons should not worry about cup design when undertaking isolated liner revision using XLPE liners.

Fiber-reinforced interim fixed dental prostheses: A clinical protocol.

Repairing or refabricating interim fixed dental prostheses can be a source of frustration in terms of lost productivity and inconvenience to the patient. The technique for reinforcing interim fixed dental prosthetic restorations described here will provide added strength and durability. The technique can be used either indirectly or for the direct intraoral fabrication of the interim prosthesis, thereby yielding predictable and esthetic results.

In vitro assessment of the marginal and internal fits of interim implant restorations fabricated with different methods.

STATEMENT OF PROBLEM: The fit of an interim implant restoration (IIR) is important for the effective treatment of patients with partial edentulism. However, no clinical trials have evaluated the marginal and internal fittings achieved with various fabrication methods. PURPOSE: The purpose of this in vitro study was to evaluate and compare the marginal and internal discrepancies in IIRs produced with 3 different methods. MATERIAL AND METHODS: Partially edentulous maxillary and mandibular casts from a transfer abutment were used. Prostheses were prepared by applying wax to the implant abutment. Shapes were copied using putty. IIRs were fabricated from poly(methyl methacrylate) for a conventional system with thermoplastic resin (CTR, n=40), a 4-axial milling machine with a crown-designed standard template library for a subtractive manufacturing system with Pekkton milling (SPM, n=40), and a 3-dimensional printer for an additive manufacturing system with digital light processing (ADL, n=40). The marginal and internal discrepancies were evaluated in each group using the silicone replica technique. The space between the abutment and the intaglio surface of the prosthesis was evaluated with a digital microscope (×160 magnification). Results were analyzed with nonparametric 2-way analysis of variance using rank-transformed values and Tukey post hoc test (α=.05). RESULTS: The fabricated IIRs were significantly different at all points (P<.001). Moreover, ADL was superior to CTR and SPM. IIRs were significantly different only at the intermarginal discrepancy (the vertical discrepancy between the crown and the point where the margin becomes round and changes to the axial wall), the axiogingival discrepancy (the vertical discrepancy between the internal surface and the axial wall adjacent to the gingival wall of the abutment), and the occlusal discrepancy (the vertical discrepancy between the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P<.001). No significant differences were found among the IIRs at the marginal discrepancy (the vertical discrepancy between the abutment margin and the crown; P>.111) and the axio-occlusal discrepancy (the vertical discrepancy between the axial wall adjacent to the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P>.257). CONCLUSIONS: ADL was superior to the other 2 fabrication methods. However, all 3 methods were suitable because they produced a marginal fit which was within the clinically acceptable range.

Site development interim removable dental prosthesis.

Transitioning a patient with partial edentulism through hard and soft tissue grafting to an implant restoration with an interim removable dental prosthesis (IRDP) presents a challenge to the restorative dentist. The management of grafted sites requires care, and without the appropriate design, an IRDP may impede surgical outcomes and place the graft at risk for displacement or necrosis. A site development IRDP (SDIRDP) for a grafted site must fulfill restorative goals and promote the surgical objectives for site development. A technique is described for fabricating an SDIRDP that facilitates surgical procedures and maintains prosthetic goals.

Cone beam computed tomography imaging as a primary diagnostic tool for computer-guided surgery and CAD-CAM interim removable and fixed dental prostheses.

This article describes a digital workflow using cone beam computed tomography imaging as the primary diagnostic tool in the virtual planning of the computer-guided surgery and fabrication of a maxillary interim complete removable dental prosthesis and mandibular interim implant-supported complete fixed dental prosthesis with computer-aided design and computer-aided manufacturing technology. Diagnostic impressions (conventional or digital) and casts are unnecessary in this proposed digital workflow, providing clinicians with an alternative treatment in the indicated clinical scenario.

Comparison of fracture loads of CAD/CAM and conventionally fabricated temporary fixed dental prostheses after different aging regimens.

This study evaluated the fracture loads of different threeunit fixed dental prostheses (FDPs) for temporary restorations. In total, three CAD/CAM materials (VITA CADTemp [CT], Telio CAD [TC], and ZENO ProFix [ZP]) and two chairside materials (Protemp 4 [PT], and Dentalon Plus [DP]) were used for the fabrication of the FDPs. Sixteen FDPs were fabricated from each material in an anatomical shape and stored in 0.9% NaCl solution at 37°C for 14 days. Thereafter, one half of the specimens from each group (n = 8) were additionally mechanically and thermally loaded (240,000 chewing cycles, 50 N, 5°/55°C, 2,100 thermal cycles). Fracture loads were measured and data analyzed using two- and one-way ANOVA, followed by Scheffé's post hoc test. ZP showed the highest mean fracture loads, regardless of the aging regime. Significantly lowest values were identified for DP and TC within the non-thermal loaded group, and for PT and CT within the thermal loaded group. No negative impact of aging regimes could be observed.