数字化口腔修复（4）-直接数字化制造

虽然口腔CAD／CAM方法依然是切削系统中的主流,但是加法制造技术也能更有效、更经济地为口腔医学提供可摘义齿支架和颅面重建的个性化固定装置。伴随更多的个性化材料的发展,修复体制造业将发生由传统的金属和陶瓷向着生物适合性的高强度聚合体、陶瓷和共熔合金方向转变。直接数字化制造将定义口腔医学的未来。数字化扫描、虚拟设计和数字化制造的进步将对传统的牙体预备,印模方法、义齿加工产生冲击。数字化的口腔技工室将经历由传统工匠向懂计算机的技师方向转变,并伴随着更先进的材料的应用,而获得高产量和高质量的回报。虽然,我们还不能够抛弃过去曾经应用于口腔医学中的常规原理,但是现在,口腔界的同仁们将为了患者去挑战和拥抱数字化口腔修复的新技术。     

Considerations About Esthetics of Composite Resin Restorations

There is a tendency to use composite resins as a universal restorative material because of the esthetics of the finished restoration. The author discusses the meaning of "esthetics" in restorative dentistry and details the clinical procedures to improve the esthetic performance of the materials. Indications for the materials are set for initial, isolated lesions in the dentition of patients who are well motivated to good standards of oral hygiene. Only then can composite resin materials be accepted as universal restorative esthetic materials, both in the front and lateral segments of the mouth.     

The effect of 0.5% sodium hypochlorite and 2% glutaraldehyde spray disenfectants on irreversible hydrocolloid impression material.

Infection control has assumed prime importance in dentistry. It is a prime concern in prosthodontics as well, where impressions materials are most commonly used. Impression materials can act as a medium for cross infection. To prevent cross infection many products are being developed. Among them 0.5% Sodium hypochlorite and 2% Glutaraldehyde are considered effective. This study was done to asses the efficacy of 0.5% Sodium hypochlorite and 2% Glutaraldehyde on irreversible hydrocolloid impression material. The result of the study indicated that they are effective against both Gram positive and Gram negative organisms and their use is recommended.     

Making a good impression: (a 'how to' paper on dental alginate)

Approximately 20,000 impressions are made with alginate annually at the University Dental Hospital of Manchester alone, and countless more wherever clinical dentistry is practised. A proportion of these are considered unsatisfactory for clinical use.The reason for these 'failures' is often poor operator technique, rather than an inherent problem of the material. With improved handling of the material and better clinical technique, failures can be avoided. This paper provides an overview of the use of alginate impression material in clinical dentistry.     

Dental materials in pediatric dentistry.

Dental materials for the restorative armamentarium in pediatric dental care continue to improve in esthetics and function. This review describes the application of some contemporary materials and concepts. Fluoride-releasing glass ionomers are appropriate for use as luting cements and as liners and bases. The glass ionomer cements have minimal solubility in oral fluids and possess the capability of inhibiting secondary caries. Amalgam and composite resin are effective for class II restorations, although amalgam placement is considerably less time consuming and less technique sensitive. Composite resins, particularly more highly filled resins, are appropriate for anterior restorative care. The use of ceramic glass inserts may provide strength and decrease restorative time for composite resin restorations in the future. When planning treatment for pediatric dental patients, each patient and restorative material to be used should be evaluated on an individual basis, in order to provide appropriate care within each material's limitations. Pediatric restorative dentistry involves the use of many materials. As materials improve in durability, strength, esthetics, and anticariogenic properties, the concepts of contemporary pediatric restorative dentistry change. Certainly, the traditional principles of restorative dentistry remain practical and significant in the practice of dentistry. Although these traditional concepts are extremely relevant, newer materials allow for modifications to be made during treatment planning in restorative dentistry. This review presents some newer materials and concepts and their applications in current pediatric restorative dentistry.     

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.     

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。     

A study on the adhesion of restorative materials to irreversible hydrocolloid impression materials

AIM: The purpose of this study was to evaluate the adhesion of restorative materials to irreversible hydrocolloid impression materials. MATERIALS AND METHODS: Three irreversible hydrocolloid impression materials were tested with four restorative materials: a base metal alloy, an amalgam, an autopolymerising resin composite and a heat polymerising resin. Samples were prepared with and without a collar. Half of the samples were cleaned with methanol by wiping. The other half were not methanol-wiped. All the samples were submerged into the impression materials and were subsequently placed in an impression- holding device in two different positions. A pullout test using a Hounsfield machine was used after the impression materials were set. RESULTS: Variance analysis was used in comparing the results obtained. Statistically, the four restorative materials showed different values regarding the adherence of the impressions materials to them (composite resin 52.47N, metal 26.36N). Samples with adherence to a collar were found to be more retentive than those without a collar. Samples with impression materials with a full collar were more retentive than those without a collar, and the samples cleaned with methanol were again less retentive than those which were not methanol wiped. CONCLUSION: The results of this study show that adhesion may be seen between restorative materials and irreversible hydrocolloid impression materials, and this adhesion may affect the accuracy of the impression.     

Are we abusing our alginate impressions? An audit

Alginate is the commonest material that is used in dentistry for impressions, but are proper clinical handling procedures being followed? This paper describes an audit of alginate impressions undertaken in an undergraduate teaching clinic to check that proper operator technique and clinical handling procedures of alginate material are in place. CLINICAL RELEVANCE: To achieve this aim, the outcome of this study is to establish a series of steps which should be followed that will assist in achieving a good impression to help undergraduates and trainee nurses in making a good alginate impression. These will form a series of guidelines based on scientific principles and best practice. Such guidelines may also be used as a teaching tool to show clinicians how to produce a clinically acceptable impression.     

Pilot study on accuracy and dimensional stability of impression materials using industrial CT technology

Objective

Using computed tomography, scan impressions can be saved and edited as virtual data. The aim of this study was to evaluate the parameters influencing different impression materials and impression trays and their relevance with regard to accuracy and dimensional stability.

Materials and methods

Two alginate impressions (Zhermack Hydrogum?5 and Kaniedenta Tetrachrom?) and a polyether impression (3MEspe Impregum?) were each combined with two acrylic trays (3M Espe Position Tray? and Profimed Opti-Tray) and CT scanned immediately after impression at the Fraunhofer Institute Development Center for X-ray Technology (EZRT) in Fürth, Germany. Each impression was digitized 10 times on the same day, 3 times after 2 days and twice after 6 days, thus determining the dimensional stability of the various materials. An acrylic model was digitized with a high-resolution ??CT research scanner to be used as a reference for assessing the accuracy of the impression materials. For graphic and statistical analysis, VGStudio Max? was used.

Results

Both alginate impressions were less dimensionally stable than the polyether impression material. The Zhermack Hydrogum?5 alginate impression resulted in more deviation (151???m) after 6 days than the Kaniedenta Tetrachrom? impression. The polyether scans showed a mean deviation of 73???m. The accuracy of both alginates was similarly precise (mean value: Hydrogum?5 0.129 ± 0.021?mm, Tetrachrom? 0.137 ± 0.002?mm). The type of tray had limited influence on the results of the alginate impressions, while the accuracy of the Impregum? impression depended on the tray combination chosen.

Conclusion

The accuracy of the alginate impressions is sufficient for clinical use in orthodontics and produced, with correct storage, acceptable results even after 2 days. Hydrogum?5 impressions proved to be slightly more accurate than the reference material but less dimensionally stable than the Tetrachrom? impressions. The 3M Espe Position Tray? seemed to be more practical due to a better retentive effect compared to the Opti-Tray made by Profimed.     

Glass ionomer cements

Glass ionomer cements have been used in pediatric restorative dentistry for 20 years. Their usefulness in pediatric restorative dentistry is preferential relative to other materials because of their fluoride release, chemical adhesion to tooth structure, and availability to use in a variety of clinical scenarios. This paper reviews the use of glass ionomer materials in pediatric restorative dentistry. The paper provides a look at glass ionomer cements' use as sealants and restorative materials and examines glass ionomers as adhesives, as a stand-alone material and in the sandwich technique. This paper also provides a useful guide to connecting to other references regarding specific aspects of glass ionomers in children.     

Comparison of impression materials for direct multi-implant impressions

STATEMENT OF PROBLEM: Given that meticulous implant prosthodontic procedures are recommended to obtain the best possible intraoral fit, impression materials that are suitable for use with a direct impression technique warrant further investigation. PURPOSE: This in vitro study compared the amount of torque required to rotate a square impression coping in an impression and evaluated the accuracy of solid implant casts fabricated from different impression materials. MATERIAL AND METHODS: Two direct transfer implant impressions were made using 8 impression materials; the torque required to rotate an impression coping in the impressions was calculated. Ten direct transfer implant impressions were made from the master model and poured in a die stone (Resin Rock) for 3 of the 8 initial impression material groups. Linear distances between steel balls placed on each abutment replica were measured with a traveling microscope to determine distortion in the impression procedure for each group. Data were analyzed (P =.05) with ANOVA and Ryan-Einot-Gabriel-Welsch multiple range test for post hoc. RESULTS: With a 1-way ANOVA, average torque values among the material groups differed significantly (P =.001). Polyether (medium consistency) was found to produce the highest overall torque values, followed by addition silicone (high consistency), and then polysulfide (medium consistency). Statistically significant difference was also found among the 3 material groups' mean absolute cast error using a 1-way ANOVA (P =.0086). Implant casts made from polyether (medium) or addition silicone (high) impressions were significantly more accurate than casts made from polysulfide medium impressions. CONCLUSION: On the basis of the results of this study, the use of either polyether (medium) or addition silicone (high) impression is recommended for direct implant impressions.     

Medium-viscosity polyether impression material: a case report

Polyethers are elastomeric materials commonly used for making precision impressions. They are hydrophilic, which facilitates the contact of the unset material with the intraoral tissue and the wetting of the impression by cast materials. The final hardness of this new impression material is reduced in an attempt to overcome rigidity of the set impression. A case is described involving the restoration of a fractured maxillary premolar and a single-phase impression technique using the new polyether impression material.     

Lithium disilicate: the restorative material of multiple options

As dentistry continues to evolve, new technologies and materials are continually being offered to the dental profession. Throughout the years restorative trends and techniques have come and gone. Some material developments have transformed the face of esthetic dentistry, while other initial concepts have already phased out and disappeared. Today, all-ceramic restorations continue to grow in the area of restorative dentistry, from pressed-ceramic techniques and materials to the growing use of zirconia, and new materials that can be created from CAD/CAM technology. This article will explore new uses for the all-ceramic material known as lithium disilicate, and the use of a digital format to design and process this material in new and exciting ways. An overview of the material as well as unique clinical procedures will be presented.     

Effect of disinfecting solutions on accuracy of alginate and elastomeric impressions

Abstract— The effect of immersion in six disinfecting solutions on the accuracy of 10 impression materials was investigated. Impressions were taken of a truncated steel cone. After setting, the impressions were either stored at room temperature for 24 h, for control, or immediately immersed in a disinfecting agent for 60 min (in one case 10 iron), and after 24 h poured with gypsum. A steel ring fitting the steel cone was placed on the resulting dies, and the discrepancy between the top surface of the ring and the die was measured. From these measurements the deviation between the base diameter of the die and of the impression was calculated to express the inaccuracy. All impressions except some in Blueprint exhibited a net shrinkage, giving rise to too large die stones and incomplete seating of the steel ring. Blueprint impressions, however, occasionally swelled and resulted in too small die stones and "overseating" of the steel ring. The disinfecting solutions had no significant impact on two impression materials. For the remaining eight materials the accuracy was decreased, increased, or unaffected by the immersion. Generally, the accuracy of the alginates investigated were more affected by the disinfecting solutions than were the elastomeric impression materials. The accuracy of the three alginates was drastically impaired by immersion in 70% ethanol, whereas the remaining five disinfecting solutions had a smaller, though sometimes statistically significant, effect on the accuracy. For the elastomeric materials only a few specific combinations of impression material and disinfecting solution reduced the accuracy. Since the control values of accuracy varied, it was concluded that the choice of elastomeric impression material is more critical than the choice of disinfecting agent. As for the alginates, brand as well as type of disinfecting solution have to be considered to obtain an acceptable accuracy of disinfected alginate impressions.     

Dimensional stability of elastomeric impression materials in custom-made and stock trays

Elastomeric impression materials for fixed prosthodontics are considered most stable when they have an even thickness of 2 to 4 mm. To obtain this, a custom-made impression tray is recommended. The purpose of the present study was to compare the stability of impressions made in custom trays and trays made of chromium-plated brass. The impression materials chosen were polyether and silicone.Two master models of the upper jaw were made of metal. The canines and first molars represented abutment teeth with flat occlusal surfaces. An engraved cross on each surface made it possible to measure in a microscope the distances between the abutment teeth on the models and in the impressions. The accuracy of the method was within ±8 μm. Twelve standardized impressions were made with each impression material in the two types of trays. The distances between the abutment teeth were measured immediately on removal of the impression, and after 1 and 24 hours. Although ample amount of impression material (2 to 9 mm) was allowed, the linear dimensional stability of the impressions made in stock trays was not inferior to the stability of impressions made in custom-made trays.     

Assessment of tissue conditioning materials for functional impressions.

The validity of two types of tissue conditioning materials was studied and compared with that of two commonly used impression materials. The effect of three important factors on the accuracy of the impressions was observed. These factors were thickness of the impression material, time of compression of the impression, and the time interval before pouring the impression. A chrome-cobalt master cast was specially designed and 500 impressions were made and poured, resulting in 900 casts. Conclusions reached from this investigation were that: 1. Visco-Gel and Coe-Comfort tissue conditioning materials can be used as impression materials. 2. The dimensional accuracy of Visco-Gel is better than that of the Coe-Comfort impressions. 3. There is no significant difference between using a tray with a space of 1.5 mm or 3.0 mm for the impression material. 4. The less bulky the impression, the less time is required for compression with fewer inaccuracies. 5. It is preferable to pour the cast in the impression immediately or within 2 hours. 6. Both kinds of materials tested can be used as duplicating materials under certain conditions.     

Adhesive dentistry and endodontics: materials, clinical strategies and procedures for restoration of access cavities: a review

The complexity of restorative dentistry has increased greatly in recent years, with the myriad of products used in "adhesive dentistry." So too has the "simple" matter of restoring access cavities after completion of endodontic treatment. This review discusses current methods of "bonding" to tooth structure, ceramic materials, and metals, with emphasis on those aspects that are important to endodontics. Specific materials, procedures and major decision making elements are discussed, as well as how to avoid problems in compatibility between endodontic and restorative materials.     

Adhesive dentistry and endodontics: materials, clinical strategies, and procedures for restoration of access cavities: a review

The complexity of restorative dentistry has increased greatly in recent years, with the myriad of products used in "adhesive dentistry." So too has the "simple" matter of restoring access cavities after completion of endodontic treatment. This review discusses current methods of "bonding" to tooth structure, ceramic materials, and metals, with emphasis on those aspects that are important to endodontics. Specific materials, procedures and major decision making elements are discussed, as well as how to avoid problems in compatibility between endodontic and restorative materials.     

Indirect composite restorations: alternative or replacement for ceramic?

In esthetic restorative dentistry, many new materials have been developed in recent years. These materials are often promoted with little clinical research and dentists use these materials on the recommendations of their peers or simply because they are new. It is the author's opinion that supportive clinical research should be examined before any material can be used with absolute confidence. In the absence of supportive research, there must be sufficient justification for trying new materials. It is the purpose of this article to examine the possible uses of indirect composite in esthetic restorative dentistry and to evaluate whether or not their use is advantageous over the use of ceramic materials.