数字化印模在口腔种植修复中的研究进展

数字化印模是指使用口内扫描仪在患者口内无需直接接触即获取组织图像,并合成三维牙列影像的印模技术。数字化印模于口腔种植修复中的应用近年来开始受到关注,但其印模精度尚不明确,尤其是多颗种植体的数字化印模精度。本文详细介绍数字化印模的原理、在种植修复不同类型牙列缺损或缺失情况下的精度以及影响精度的相关因素,以期为数字化印模在种植修复中的临床应用提供参考依据。     

Nontraumatic Final Impressions for Fixed Partial Dentures

A nontraumatic, nonretraction impression technique is presented which uses the fabrication of an acrylic resin shell from an interocclusal wax impression. A crucial step in the procedure is obtaining the complete finish line of the preparation within the resin. This tray, which is filled with an elastomeric impression material, is combined with a triple tray of the same material to provide all the necessary relationships to construct a crown or coping. This procedure is especially efficient for multiple abutments during fixed partial denture construction.     

Impression Technique for Arches Requiring Both Implant and Natural Tooth Restorations

Implant impression copings reduce access to prepared teeth during the impression-making process. If the impression copings and teeth are in close proximity, it may be difficult to extrude impression material circumferentially around the margins of the tooth preparations. A technique is described that allows the impressions of the prepared teeth to be made without the implant impression copings interfering. The advantages and disadvantages of the technique are discussed.     

Dimensional change of impressions on sterilization

The volume of impressions, before and after disinfection in a gluteraldehyde solution for longer than ten hours (that is, sterilization), was measured indirectly from dies produced from the impressions. Three elastomeric impression materials were used in both acrylic resin and poly-vinyl-chloride 'trays' to form the impressions. One impression material appeared to be practically superior to the others with respect to variability of volume. The effect of tray material on change in volume (calculated as after disinfection minus before disinfection) was significant for one impression material; acrylic trays produced the greatest effect. The change in volume was significant for two impression materials; acrylic trays were associated with greater increase in volume. It was concluded that if impressions are to be sterilized, a tray material having minimal potential to absorb disinfectant should be used.     

Evaluation of Polycaprolaitone Custom Tray Material

Custom impression trays are necessary for accurate impressions in fixed prosthodontics when using polysulfide impression materials. These custom impression trays are needed to provide for a uniform thickness of impression material to minimize distortion. Custom impression trays have historically been made from acrylic resin. New materials have been developed as alternatives to acrylic resin, and this study evaluates one product currently available that is composed of polycaprolaitone. This study evaluates the modulus of elasticity of polycaprolaitone as compared with acrylic resin, and also evaluates the amount of permanent deformation of the new material when placed under a load. The elastic modulus of polycaprolaitone was tested using three-point bending of specimens placed in a universal mechanical test system. The elastic modulus of the new material was found to be significantly lower than that of acrylic resin. The next test evaluated the amount of permanent deformation of the polycaprolaitone material when specimens approximating the shape and size of custom impression trays were placed under a load. These trays were placed in a universal mechanical test system and differing loads were placed on them. Results showed that although the trays deformed at relatively low loads, all deformation was fully recovered within a clinically insignificant period of time (less than 30 seconds). From these experiments it was concluded that although the polycaprolaitone material has a lower modulus of elasticity and will deform under relatively low loads, the material recovers completely, and thus the deformation would not interfere with the clinical performance of polycaprolaitone as a custom tray material.     

The Digital One‐Abutment/One‐Time Concept. A Clinical Report

The digital fabrication of dental restorations on implants has become a standard procedure during the last decade. Avoiding changing abutments during prosthetic treatment has been shown to be superior to the traditional protocol. The presented concept for implant‐supported single crowns describes a digital approach without a physical model from implant placement to final delivery in two appointments. A 54‐year‐old man was provided with a single‐tooth implant on his left mandibular first molar. Before wound closure, the implant position was captured digitally with an intraoral scanning device. After bone healing at the time of second‐stage surgery the final screw‐retained crown fabricated without a physical model was inserted. Soft tissue healing took place at the definitive restoration, avoiding abutment changes or changes of the healing cap. These led to stable soft tissues with a minimum of surgery. The benefits of digital fabrication and the unique way to scan the implant right after placement give an additional value that would not be achieved by analog techniques. In addition to financial benefits it represents a biologically advantageous, one‐abutment/one‐time approach with customized screw‐retained, full‐contour crowns or cemented crowns on custom abutments.     

The Accuracy of Six Impression Techniques for Osseointegrated Implants

Purpose Six impression techniques were evaluated using tapered and square impression copings. Materials and Methods The absolute distortion was measured using a cast metal impression tray with fiduciary reference points external to the impression material. Measurements of the x, y, z coordinates on the master cast and the impressions were directly made with a travelling digitizing microscope. The difference between the coordinates of each of six sites in the impression and the corresponding reference site were compared. Results There was no significant difference between the techniques for the square copings but that there was a significant loss of accuracy in the z-axis with the tapered copings. Conclusions No significant differences were noted.     

Prosthodontic procedures for implant reconstruction. 2. Post-surgical procedures

There is essentially no flexibility in an osseo-integrated implant system, so that the final fit of the prosthesis must be absolutely precise. A simple approach to this problem is presented with details as to impression taking, confirmation of accuracy of the master cast, fitting of the cast metal framework and construction of the superstructure. The information presented describes a full arch fixed restoration attached to mandibular implants, but may easily be followed for the maxilla or modified for quadrant restorations.     

Disinfection procedures: their efficacy and effect on dimensional accuracy and surface quality of an irreversible hydrocolloid impression material

Objectives

This study investigated the antibacterial efficacy and effect of 0.55% ortho-phthalaldehyde (Cidex OPA^®) and 0.5% sodium hypochlorite (NaOCl) on the dimensional accuracy and surface quality of gypsum casts retrieved from an irreversible hydrocolloid impression material.

Methods

A simulated clinical cast and technique was developed to compare the dimensional accuracy and surface quality changes of the test gypsum casts with controls. Dimensional accuracy measurements were completed between fixed points using a travelling microscope under low angle illumination at a magnification of ×3. Surface quality changes of “smooth” and “rough” areas on the cast were evaluated by means of optical profilometry. The efficacy of the disinfection procedures against Pseudomonas aeruginosa was evaluated by determining the number of colony forming units (cfu) recovered after disinfection of alginate discs inoculated with 1 × 10⁶ cfu for defined intervals.

Results

The dimensional accuracy of the gypsum casts was not significantly affected by the disinfection protocols. Neither disinfectant solution nor immersion time had an effect on the surface roughness of the “smooth” area on the cast, however, a significant increase in surface roughness was observed with increasing immersion time for the “rough” surface. Complete elimination of viable Pseudomonas aeruginosa cells from alginate discs was obtained after 30 and 120 s immersion in Cidex OPA^® and NaOCl, respectively.

Conclusions

Immersion of irreversible hydrocolloid impressions in Cidex OPA^® for 30 s was proved to be the most effective disinfection procedure.     

Dental specialty,career preferences and their influencing factors among final year dental students in Saudi Arabia

Objective

The purpose of this study was to investigate evolving trends in dental post graduate specialty preferences and career aspirations among final year dental students in Saudi Arabia.

Evaluation of Dimensional Stability and Accuracy of Autoclavable Polyvinyl Siloxane Impression Material

Dimensionally stable autoclavable impressions will be effective in controlling the cross-infection and contamination caused by patient’s saliva and other oral secretions. The accuracy of newly introduced autoclavable polyvinyl siloxane impression material was assessed for its dimensional stability and accuracy. A standard metal model (Dentoform, U-501, Columbia) was customised for impression making. The impressions were made using the newly introduced polyvinyl siloxane impression materials (AFFINIS, Coltene/Whaledent AG, 9450 Alstalten, Switzerland). Fifty impressions were made and were divided into two groups A and B of 25 each. Group A was the control sample (non-autoclaved impressions) and group B was the test sample (autoclaved impressions), which was subjected to the steam autoclave procedure at 134 °C for 18 min, casts were poured in type IV gypsum products. The customised metal model, casts obtained from control and test group were subjected to laboratory evaluation with help of a travelling microscope (×10 magnification), and digital vernier calliper (0.01 mm/10 μm accuracy). Data analysis was done using one-way ANOVA and One-Sample t test to evaluate the overall accuracy (P < 0.005). As a result, there was an average reduction of 0.016 μm in overall dimension between the test and the control group when compared with the master model, which is not statistically or clinically significant. The newly introduced polyvinyl siloxane impression material is accurate and dimensional stable for clinical use when steam autoclaved at 134 °C for 18 min.     

数字化口腔修复(2)——数字化印模

义齿采用数字化的加工方法,有助于提高修复体质量,改善护理质量,并为患者提供最佳就诊体验.数字化印模易于储存,不占空间,且无需消毒,极大地避免了气泡、裂痕和收缩变形的发生.随着新技术的迅猛发展,优化数字化印模的操作,降低数字化印模的成本,将有助于其发展.     

Physicochemical and mechanical characterization of a fiber-reinforced composite used as frameworks of implant-supported prostheses

ObjectivesTo characterize the physicochemical and mechanical properties of a milled fiber-reinforced composite (FRC) for implant-supported fixed dental prostheses (FDPs).MethodsFor FRC characterization, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction, Fourier-transformed infrared spectrometry, simultaneous thermogravimetric analysis and differential scanning calorimetry were performed. For fatigue testing, 3-unit FRC frameworks were fabricated with conventional (9 mm² connector area) and modified designs (12 mm² connector area and 2.5 mm-height lingual extension). A hybrid resin composite was veneered onto the frameworks. FDPs were subjected to step-stress accelerated-life fatigue testing until fracture or suspension. Use level probability Weibull curves at 300 N were plotted and the reliability for 100,000 cycles at 300, 600 and 800 N was calculated. Fractographic analysis was performed by stereomicroscope and SEM.ResultsThe FRC consisted of an epoxy resin (∼25%) matrix reinforced with inorganic particles and glass fibers (∼75%). Multi-layer continuous regular-geometry fibers were densely arranged in a parallel and bidirectional fashion in the resin matrix. Fatigue analysis demonstrated high probability of survival (99%) for FDPs at 300 N, irrespective of framework design. Conventional FDPs showed a progressive decrease in the reliability at 600 (84%) and 800 N (19%), whereas modified FDPs reliability significantly reduced only at 800 N (75%). The chief failure modes for FRC FDPs were cohesive fracture of the veneering composite on lower loads and adhesive fracture of the veneering composite at higher loads.SignificanceMilled epoxy resin matrix reinforced with glass fibers composite resulted in high probability of survival in the implant-supported prosthesis scenario.     

Impression technique for monitoring and virtual treatment planning in nasoalveolar moulding

We describe our experience with various silicone materials for making one-step and two-step impressions of the cleft-lip-palate-nose complex during nasoalveolar moulding. Our technique is superior to common alginate-based impression techniques, as it provides precise reproduction of the complex anatomy of the cleft, and is compatible with the latest available methods of planning treatment with nasoalveolar moulding, such as computer-aided reverse engineering and rapid prototyping.