Ju-Mi Park

Effect of impression coping and implant angulation on the accuracy of implant impressions: an in vitro study

PURPOSE The purpose of this study was to compare the accuracy of the implant master cast according to the type (pick-up, transfer) and the length (long, short) of the impression copings. MATERIALS AND METHODS The metal master cast was fabricated with three internal connection type implant analogs (Osstem GS III analog), embedded parallel and with 10° of mesial angulation to the center analog. Four types of impression coping were prepared with different combinations of types (transfer, pick-up) and lengths (long, short) of the coping. The impressions were made using vinyl polysiloxane (one step, heavy + light body) with an individual tray, and 10 impressions were made for each group. Eventually, 40 experimental casts were produced. Then, the difference in the distance between the master cast and the experimental cast were measured, and the error rate was determined. The analysis of variance was performed using the SPSS (v 12.0) program (α = .05), and the statistical significance was set at P < .05. RESULTS The ANOVA showed that the pick-up type impression coping exhibited a significantly lower error rate than the transfer type. However, no significant difference was observed with respect to the length of the impression coping. Additionally, no significant difference was observed between the parallel and mesial angulated groups. CONCLUSION Within the limitations of this study, the pick-up type impression coping exhibited a more accurate implant master cast than the transfer type in parallel group. The accuracy of the implant master cast did not differ for different lengths of impression coping of at least 11 mm. Additionally, the accuracy of the implant cast was not different for the parallel and 10° mesial angulated groups.

Evaluation of in vitro and in vivo tests for surface-modified titanium by H2SO4 and H2O2 treatment

Titanium is widely used as an implant material for artificial teeth. Furthermore, various studies have examined surface treatment with respect to the formation of a fine passive film on the surface of commercial titanium and its alloys and to improve the bioactivity with bone. However, there is insufficient data about the biocompatibility of implant materials in the body. The purpose of this study was to examine whether surface modification affects the precipitation of apatite on titanium metal. Specimens were chemically washed for 2 min in a 1∶1∶1.5 (vol.%) mixture of 48 %HF, 60%HNO3 and distilled water. The specimens were then chemically treated with a solution containing 97%H2SO4 and 30%H2O2 at the ratio of 1∶1 (vol.%) at 40°C for 1h, and subsequently heat-treated at 400°C for 1h. All the specimens were immersed in HBSS with pH 7.4 at 36.5°C for 15d, and the surface was examined with TF-XRD, SEM, EDX and XPS. In addition, specimens of commercial pure Ti, with and without surface treatment, were implanted in the abdominal connective tissue of mice for 28 d. Conventional aluminum and stainless steel 316L were also implanted for comparison. An amorphous titania gel layer was formed on the titanium surface after the titanium specimen was treated with a solution of H2SO4 and H2O2. The average roughness was 2.175 μm after chemical surface treatment. The amorphous titania was subsequently transformed into anatase by heat treatment at 400°C for 1h. The average thickness of the fibrous capsule surrounding the specimens implanted in the connective tissue was 47.1μm in the chemically treated Ti, and 52.2, 168.7 and 101.9μm, respectively, in the untreated commercial pure Ti, aluminum and stainless steel 316L.

Evaluation of shear bond strength between dual cure resin cement and zirconia ceramic after thermocycling treatment

PURPOSE This study was performed to evaluate shear bond strength (SBS) between three dual-cured resin cements and silica coated zirconia, before and after thermocycling treatment. MATERIALS AND METHODS Sixty specimens were cut in 15 × 2.75 mm discs using zirconia. After air blasting of 50 µm alumina, samples were prepared by tribochemical silica coating with Rocatec™ plus. The specimens were divided into three groups according to the dual-cure resin cement used: (1) Calibra silane+Calibra®, (2) Monobond S+Multilink® N and (3) ESPN sil+RelyX™ Unicem Clicker. After the resin cement was bonded to the zirconia using a Teflon mold, photopolymerization was carried out. Only 10 specimens in each group were thermocycled 6,000 times. Depending on thermocycling treatment, each group was divided into two subgroups (n=10) and SBS was measured by applying force at the speed of 1 mm/min using a universal testing machine. To find out the differences in SBS according to the types of cements and thermocycling using the SPSS, two-way ANOVA was conducted and post-hoc analysis was performed by Turkeys test. RESULTS In non-thermal aged groups, SBS of Multilink group (M1) was higher than that of Calibra (C1) and Unicem (U1) group (P<.05). Moreover, even after thermocycling treatment, SBS of Multilink group (M2) was higher than the other groups (C2 and U2). All three cements showed lower SBS after the thermocycling than before the treatments. But Multilink and Unicem had a significant difference (P<.05). CONCLUSION In this experiment, Multilink showed the highest SBS before and after thermocycling. Also, bond strengths of all three cements decreased after thermocycling.

Impact of implant support on mandibular free-end base removable partial denture: theoretical study

OBJECTIVES This study investigated the impact of implant support on the development of shear force and bending moment in mandibular free-end base removable partial dentures (RPDs). MATERIAL AND METHODS Three theoretical test models of unilateral mandibular free-end base RPDs were constructed to represent the base of tooth replacement, as follows: Model 1: first and second molars (M1 and M2); Model 2: second premolar (P2), M1, and M2; and Model 3: first premolar (P1), P2, M1, and M2. The implant support located either at M1 or M2 sites. The occlusal loading was concentrated at each replacement tooth to calculate the stress resultants developed in the RPD models using the free-body diagrams of shear force and bending moment. RESULTS There was a trend of reduction in the peak shear force and bending moment when the base was supported by implant. However, the degree of reduction varied with the location of implant support. The moment reduced by 76% in Model 1, 58% in Model 2, and 42% in Model 3, when the implant location shifted from M1 to M2 sites. CONCLUSIONS The shear forces and bending moments subjected to mandibular free-end base RPDs were found to decrease with the addition of implant support. However, the impact of implant support varied with the location of implant in this theoretical study.

Evaluation of effect of galvanic corrosion between nickel-chromium metal and titanium on ion release and cell toxicity

PURPOSE The purpose of this study was to evaluate cell toxicity due to ion release caused by galvanic corrosion as a result of contact between base metal and titanium. MATERIALS AND METHODS It was hypothesized that Nickel (Ni)-Chromium (Cr) alloys with different compositions possess different corrosion resistances when contacted with titanium abutment, and therefore in this study, specimens (10×10×1.5 mm) were fabricated using commercial pure titanium and 3 different types of Ni-Cr alloys (T3, Tilite, Bella bond plus) commonly used for metal ceramic restorations. The specimens were divided into 6 groups according to the composition of Ni-Cr alloy and contact with titanium. The experimental groups were in direct contact with titanium and the control groups were not. After the samples were immersed in the culture medium - Dulbeccos modified Eagles medium[DMEM] for 48 hours, the released metal ions were detected using inductively coupled plasma mass spectrometer (ICP-MS) and analyzed by the Kruskal-Wallis and Mann-Whitney test (P<.05). Mouse L-929 fibroblast cells were used for cell toxicity evaluation. The cell toxicity of specimens was measured by the 3-{4,5-dimethylthiazol-2yl}-2,5-diphenyltetrazolium bromide (MTT) test. Results of MTT assay were statistically analyzed by the two-way ANOVA test (P<.05). Post-hoc multiple comparisons were conducted using Tukeys tests. RESULTS The amount of metal ions released by galvanic corrosion due to contact between the base metal alloy and titanium was increased in all of the specimens. In the cytotoxicity test, the two-way ANOVA showed a significant effect of the alloy type and galvanic corrosion for cytotoxicity (P<.001). The relative cell growth rate (RGR) was decreased further on the groups in contact with titanium (P<.05). CONCLUSION The release of metal ions was increased by galvanic corrosion due to contact between base metal and titanium, and it can cause adverse effects on the tissue around the implant by inducing cytotoxicity.

Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia. MATERIALS AND METHODS Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (α≤.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (α≤.05). RESULTS The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups. CONCLUSION The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.

Prosthodontic treatment of a retrognathic edentulous maxilla demonstrating limited interarch distance: 3.5-year results with fixed and removable implant prostheses

The prosthodontic treatment of patients with a retrognathic edentulous maxilla should consider the restoration of the lower facial profile and access for oral hygiene. This clinical report describes prosthodontic treatments of a patient with edentulism who presented with repeated fractures of the denture teeth of a maxillary implant-supported complete fixed dental prosthesis (ICFDP) and a mandibular implant-supported overdenture. Considerable plaque accumulation was noted on the ICFDP, which was replaced with an open palatal design implant-supported overdenture. However, the patient experienced difficulty managing the 2 removable prostheses. The patients mandible was eventually restored with a milled titanium alloy framework ICFDP with metal occlusal surfaces. This combined approach of fixed and removable prostheses was stable at 3.5-year follow-up appointment, without compromising the patients oral hygiene or comfort.

Expedited Record Base Fabrication Using an Irreversible Hydrocolloid Cast

The registration of a maxillomandibular relationship requires additional clinical and laboratory procedures when the mouth presents with loss of occlusal support. This procedure can be a challenge for a patient who needs urgent care or resides in a remote area. This article describes a procedure for expediting the mounting of a master cast for the fabrication of a maxillary immediate complete denture. The technique presented describes the use of a silicone record base made on an irreversible hydrocolloid cast generated from the final impression.

Use of irreversible hydrocolloid impression material to correct a defect in complete denture definitive impressions

Figure 1.Maxillary PVS impression demonstrating defect in palatal region. A maxillary complete denture (CD) impression often demonstrates a defect in the palatal region of the edentulous arch. This problem commonly relates to air trapped in the impression material or mishandling of the tray seating; the bubble formed in the impression can compromise the fit of the CD or impair tissue health. One method of correcting the impression when the defect is small and localized is to use a dental impression wax. This procedure requires the impression wax to fill the defect and the impression to be seated and separated repeatedly until the wax presents the surface detail of the mucosa without overlapping the adjacent impression surface. However, errors may develop because of poor handling and misjudgments such as displacement of the mucosa and distortion of the wax upon removal from the mouth. The impression is often relined with a light-viscosity impression material. This method is convenient and eliminates the risk of reproducing the error in another impression. However, the relining procedure may subject the mucosa of the palatal vault to excessive hydraulic pressure and cause tissue displacement. At removal, the impression may demonstrate poorly developed borders at the periphery, and the fit and retention of the denture will be compromised. An alternative procedure for correcting polyvinyl siloxane (PVS) definitive CD impressions with an irreversible hydrocolloid impression material is presented. When a defect is identified, 2 small holes are made in a diagonal direction through the tray. With the impression seated intraorally, the secondary impression material is injected into the defect through a hole until the excess is extruded through the other.

Indirect method of base adaptation against supporting element of tooth root for a partial overdenture prosthesis

The base of a partial overdenture prosthesis should be fitted intraorally against the supporting element of a tooth root. Chairside relining is a common method; however, an autopolymerizing acrylic resin presents high porosity when polymerized intraorally. This article describes an indirect method where an impression is made with a silicone occlusion registration material to create a replica of the supporting elements of the residual ridge and the tooth root in a high-viscosity polyvinyl siloxane impression material.