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PubMed2006

A finite element analysis of ferrule design on restoration resistance and distribution of stress within a root.

AIM: To analyse the effect of ferrule height upon the mechanical resistance and stress distribution within a root to explain variations in the pattern of root fracture. METHODOLOGY: An extracted, intact, caries free, maxillary right central incisor was scanned by laser and then reconstructed on a computer to produce a model of the tooth and associated periodontal ligament. A simulated post/core/crown restoration was constructed on conventional tooth preparations with various ferrules. The crown was loaded with a simulated 500 N force and the simulated displacement of components and the tensile and compressive stress within the tooth structure were recorded. RESULTS: Without a ferrule preparation, the simulated crown tilted to the labial and rotated distally. With increasing ferrule height the displacement and rotation of the crown reduced in conventional and crown-lengthening models with maximum reduction occurring when the ferrule height reached 1.5 mm. In ferrule models, higher levels of tensile stress developed in internal (by a factor of 8) and mid-root palatal (by a factor of 90) dentine at the cervical margin of the preparation. With an increase in ferrule height, the area of tensile stress within the palatal mid-dentine expanded towards the cervical margin. Similar patterns and stress values were recorded for the crown-lengthening models. CONCLUSION: The study confirms that a ferrule increases the mechanical resistance of a post/core/crown restoration. However a ferrule creates a larger area of palatal dentine under tensile stress that may be a favourable condition for a crack to develop. Crown-lengthening did not alter the levels or pattern of stress within compared with conventional ferrule preparations.

Computer Simulation↗
PubMed1999

Resin-bonded prostheses: the current state of development.

In the 25 years since the first resin-bonded prosthesis was described, this adhesive technique for splinting mobile teeth has developed into a conservative method for replacing missing teeth. There was a high debond rate associated with the early resin-bonded prostheses, which led many clinicians to question their clinical appropriateness for long-term use. These early failures were attributed to the limited bond strength between the metalwork and etched enamel. Despite improvements in the adhesive bond strengths, there was still an unacceptable number of clinical debonds. The biomechanical design of resin-bonded prostheses did not develop with the same rapidity or with the same predictability as did the advancements with the associated adhesive technology. Through ongoing development, studies have shown various biomechanical designs that may improve clinical retention. The purpose of this article is to examine the biomechanical principles for current resin-bonded prosthesis design, including aspects of tooth preparation and framework design that will improve clinical retention.

Animals↗
PubMed2003

Class IV preparations for fractured anterior teeth restored with composite resin restorations.

Pediatric dentists play a major role in treating most of the anterior teeth fractures due to the fact that most patients who suffer such traumatic injuries are between the ages of seven and fourteen. Several techniques has been developed to restore the fractured incisors to the original shape and color, these include full-coverage of the traumatized tooth, or restoring the incisors with a resin. The purpose of this study is to find the ideal combination of tooth preparation and restorative material, namely, to determine if stair step chamfer preparations provide more retention in class IV restorations than the plain chamfer preparation technique when restored with a combination of a hybrid composite resin and a microfilled composite resin. This was done by comparing the shear strength values between the buccal stair-step chamfer preparation, and a modification on it (buccal and lingual stair-step chamfer preparation) and the plain chamfer preparation techniques in class IV restorations on anterior incisors using different composite resin materials. The Instron machine was used to test shear strength. One hundred and two bovine incisor teeth were freshly harvested from the slaughterhouse. The teeth were prepared and restored according to the following six groups; Plain Chamfer preparation with Tetric Ceram Composite, Plain Chamfer preparation with Renamel Composite, buccal stair-step chamfer preparation with Tetric Ceram composite, buccal stair-step chamfer preparation with Renamel composite, Buccal and lingual stair-step preparation with Tetric Ceram Composite, Buccal and lingual stair-step chamfer preparation with renamel composite. All samples were fractured using the Instron testing machine then the surface area were measured using Image-J software. Shear strength for every sample was calculated using the load numeric result from the Instron machine and the measured surface area. The Two-Factorial (AB) Analysis of Variance For Independent Samples showed that the buccal stair-step chamfer preparation showed significantly higher shear strength and fracture resistance than plain chamfer or the buccal and lingual stair-step chamfer preparation. The combination of Renamel Hybrid and Renamel Microfill composite materials showed better results than the Tetric Ceram composite when used with all three preparation techniques, but did not show a statistical significance. It was concluded that buccal stair-step preparation technique provided the ideal preparation technique with bonded composite resins in fractured anterior teeth. Only 7% of the entire sample size had an adhesion failure versus 93% that had cohesion failure. There was no significant difference in shear strength, between the restorative materials used, in conjunction with all the preparation techniques.

Analysis of Variance↗
PubMed1998

[Histologic study on the pulpal response after complete crown preparation].

Protecting pulp health during preparation procedures is one of the key factors for prosthesis success. The histological sections of dental pulp showed the disruption of odontoblastic layer, blood vessels hyperemia and local bleeding. Dental histological sections of 40 healthy teeth which would need to be detracted because of orthodontical treatment were made to observe the pulp response in vivo during different tooth preparation time, including four groups: before preparation, after preparation, one week after being covered with temporary crown and two weeks after being covered with temporary crown. when air-water spray was used during crown preparation, Healing of the pulp was apparent 2 weeks following preparation, when the prepared teeth were covered with temporary crown and cemented with zinc oxide eugenol.

Crowns↗
PubMed2004

Proximal margin modifications for all-ceramic veneers.

Conventional ceramic veneers circumvent contact areas and extend palatally in the gingival third of the tooth only. Veneers are no longer considered reversible therapy. With the objective of longevity in mind, proximal extensions beyond contact areas maximize the functional and aesthetic potential of veneers and maintain conservative tooth preparations. The clinical and laboratory advantages of proximal veneer extensions for anterior teeth significantly outweigh the disadvantage of increased tooth structure removal. This article presents a modified preparation technique for the proximal extension of ceramic veneer preparations in the anterior region.

Dental Porcelain↗
PubMed1995

Effects of relining on long-term marginal stability of provisional crowns.

Provisional resins crowns are commonly placed to protect prepared teeth, but the marginal adaptation of interim crowns has always been a problem. These experiments examined the effects of thermocycling and occlusal loading on relined and unrelined polymethyl methacrylate resin transitional crowns. Three groups of interim crowns were made on a cast metal die tooth preparation; unrelined, relined correction, and paint-on correction. After thermocycling and occlusal loading of the specimens, the change in mean marginal gap was significantly greater for the unrelined group. Axial changes were greatest for relined group and least for the unrelined group. These results suggested that relining of polymethyl methacrylate interim crowns can be useful to prevent increases in marginal gap width during extended intraoral periods.

Analysis of Variance↗
PubMed2005

Treatment of extended anterior crown fractures using Type IIIA bonded porcelain restorations.

Novel-design bonded porcelain restorations, the so-called Type IIIA BPRs, represent a reliable and effective procedure when restoring large parts of the coronal volume and length in the anterior dentition. While traditional treatment approaches involve the removal of large amounts of sound tooth substance (with adverse effects on the pulp, gingivae and crown biomechanics, as well as serious financial consequences), the use of adhesive technology instead can provide maximum preservation of tissues and limited costs. Considerable advantages, such as the economical and noninvasive treatment of crown-fractured teeth, are inherent to Type IIIA bonded porcelain restorations, reducing the need for preprosthetic interventions (e.g., root canal therapy and crown-lengthening) and the use of intraradicular posts. This article, illustrated with cases with up to eight and 10 years' follow-up, sets the scientific foundations of this concept, as well as important considerations about function, strength, tooth preparation, laboratory technique, and bonding optimization.

Adolescent↗
PubMed2000

Restoring esthetics and anterior guidance in worn anterior teeth. A conservative multidisciplinary approach.

BACKGROUND: Developments in adhesive dentistry have given the dental profession new restorative materials and technology to restore esthetics and function to the worn anterior dentition. This article illustrates, through a clinical case study, the clinical requirements for restoring esthetic harmony and functional stability to the worn anterior dentition. CASE DESCRIPTION: The author presents the case of a 24-year-old man who sought esthetic dental treatment because he was unhappy with the appearance of his maxillary anterior teeth. The review of his dental history revealed that he ground his teeth at night. The author performed a complete evaluation of the causes of the patient's bruxism and created a diagnostic preview to, among other things, develop the relationship between the condylar and anterior guidance and to establish the esthetic requirements for the final restorations. Treatment included periodontal recontouring, tooth preparation and placement of temporary and then permanent restorations; the patient also was given an occlusal guard to protect the restorations against future bruxing. CLINICAL IMPLICATIONS: Whatever the cause of occlusal instability, it is important that the restorative dentist be able to recognize its signs--such as tooth hypermobility, tooth wear, periodontal breakdown, occlusal dimpling, stress fractures, exostosis, muscle enlargement and loss of posterior disclusion. When restoring the worn dentition, the clinician should bear in mind the five P's: proper planning prevents poor performance.

Adult↗
PubMed2005

Clinical considerations for densely sintered alumina and zirconia restorations: Part 1.

Densely sintered alumina- and zirconia-based restorations were introduced to dentistry in the early 1990s and became a popular treatment modality, especially in situations requiring complete-coverage restorations. The use of industrial technologies for the fabrication of the restoration, simple clinical management, and pleasing esthetic outcome have made these restorations an attractive treatment alternative. This article reviews the nature of the materials used and the technologies involved and provides indications for clinical case selection and tooth preparation.

Adult↗
PubMed2002

[Advancements in dental preparation technique (literature review)].

This paper has reviewed the literature on the methods of cavity preparation. The different methods are summarised in Table 1. Nowadays rotary instruments are accepted as standard for cavity preparation. The limitation of using a rotary instrument is the iatrogenic damage to adjacent teeth. Therefore some of the hand instruments remained an essential part of quality restorative dentistry. In order to reduce iatrogenic injury oscillating instruments had been developed. The oscillating instruments change the rotary movement into an oscillating movement and copy the shape of the working tip through an abrasive medium to the tooth surface. The abrasive medium is generally diamond. A new possibility in tooth preparation is the Er:YAG laser. It can be used for both cavity preparation and caries removal. The chemo-mechanical caries removal means the selective chemical softening is followed by the mechanical removing of carious dentin.

Dental Caries↗
PubMed1996

Cutting effectiveness of diamond points on commercial core composite resins and cements.

In dental clinics, composite resin and cement cores are routinely cut and polished during abutment tooth preparation. To identify their characteristics during cutting, weight-load cutting tests were performed on eight commercial core composites and two cements, using diamond points driven by an air-turbine handpiece. It became evident that the cutting effectiveness of the diamond points on nine workpieces exceeded that on natural tooth dentine, while that on one composite containing Si3,N4 filler was analogous to that on dentine. With continued use, the cutting effectiveness of the diamond point on all workpieces gradually declined. SEM observations revealed that diamond particles of the diamond point wore out with repeated use. It is clinically advised to select the core material with material characteristics during cutting and mechanical strength similar to those of dentin.

Animals↗
PubMed2001

Retrospective assessment of 546 all-ceramic anterior and posterior crowns in a general practice.

STATEMENT OF PROBLEM: There is need to determine whether following a consistent procedural protocol in a private dental practice will result in high success rates for all-ceramic anterior and posterior crowns fabricated from aluminous porcelain veneered to high-alumina content-supporting cores. Aluminous porcelain is known to have poor tensile strength and fracture resistance when subjected to shear forces. PURPOSE: This study examined the long-term survivability of alumina core, all-ceramic crowns in both anterior and posterior locations. MATERIAL AND METHODS: Following a consistent protocol over 6 years, 546 all-ceramic, In-Ceram crowns (32.4% anterior [n = 177] and 67.6% posterior [n = 369]) were consecutively luted with glass ionomer resin hybrid cement and periodically observed by the same dentist who prepared and cemented them. RESULTS: The overall success rate was 99.1% (n = 541) with a 0.9% (n = 5) failure rate. The success-to-failure ratio for anterior all-ceramic crowns was 98.9% to 1.1% (n = 175:2); the posterior crown ratio was 99.2% to 0.8% (n = 366:3). CONCLUSION: Following a consistent protocol of careful tooth preparation and crown cementation resulted in high success rates for anterior and posterior all-ceramic crowns. Glass ionomer resin hybrid cement appeared to be a reliable luting agent. All-ceramic alumina core crowns are durable and provide optimum esthetic choices for anterior and posterior locations.

Aluminum Oxide↗
PubMed2001

Periodontal considerations in restorative and implant therapy.

The successful integration of periodontal and restorative dentistry for both natural teeth and implants requires knowledge and application of both mechanical and biological principles. In areas of aesthetic concern, an adequate band of attached gingiva can increase patient comfort, reduce the probability of gingival recession following tooth preparation and simplify restorative procedures. While some restorative margins need to be placed at or below the margin of the free gingiva, this should be considered to be a compromise, and margins should not be placed more than 0.5 mm into a healthy gingival sulcus. Approximately 2-3 mm of healthy, natural supra-alveolar tooth surface is needed for attachment of the gingival tissues to the tooth. This dimension is called the biological width. If adequate biological width does not exist, surgical or orthodontic procedures to expose healthy tooth structure are recommended before final restorations are placed. Retraction of soft tissues for impressions is best accomplished with mechanical methods rather than lasers or electrosurgery because of the potentially harmful effects of these devices to the cementum, bone and soft tissues surrounding the teeth. Implants function best and withstand occlusal forces optimally when loaded in a vertical direction. Therefore, planning implant placement is critical for success. Because of increased proprioception, it is suggested that natural teeth be used to guide the occlusion in partially edentulous patients. Cantilevers should be used with caution and with appropriate attention to occlusal forces. While occlusal trauma does not cause periodontal disease, it may contribute to bone loss around teeth and implants. In the opinion of the authors, provisional restorations are an integral part of dental and periodontal therapy. They can be used to establish aesthetic and physiological contours that can be easily cleaned by patients and they can also be used as a guide for any needed surgical tissue modification.

Crown Lengthening↗
PubMed1998

Indentation damage and mechanical properties of human enamel and dentin.

Understanding the mechanical properties of human teeth is important to clinical tooth preparation and to the development of "tooth-like" restorative materials. Previous studies have focused on the macroscopic fracture behavior of enamel and dentin. In the present study, we performed indentation studies to understand the microfracture and deformation and the microcrack-microstructure interactions of teeth. It was hypothesized that crack propagation would be influenced by enamel rods and the dentino-enamel junction (DEJ), and the mechanical properties would be influenced by enamel rod orientation and tooth-to-tooth variation. Twenty-eight human third molars were used for the measurement of hardness, fracture toughness, elastic modulus, and energy absorbed during indentation. We examined the effect of enamel rod orientation by propagating cracks in the occlusal surface, and in the axial section in directions parallel and perpendicular to the occlusal surface. The results showed that the cracks in the enamel axial section were significantly longer in the direction perpendicular to the occlusal surface than parallel. The cracks propagating toward the DEJ were always arrested and unable to penetrate dentin. The fracture toughness of enamel was not single-valued but varied by a factor of three as a function of enamel rod orientation. The elastic modulus of enamel showed a significant difference between the occlusal surface and the axial section. It is concluded that the cracks strongly interact with the DEJ and the enamel rods, and that the mechanical properties of teeth are functions of microstructural orientations; hence, single values of properties (e.g., a single toughness value or a single modulus value) should not be used without information on microstructural orientation.

Analysis of Variance↗
PubMed1999

1-year clinical evaluation of Compoglass and Fuji II LC in cervical erosion/abfraction lesions.

PURPOSE: This study was undertaken to compare the clinical performance of a polyacid-modified resin-based composite and a resin-modified glass-ionomer restorative material over 1 year. MATERIALS AND METHODS: Thirty-four pairs of restorations of Compoglass (C) and Fuji II LC (F) were placed in 31 patients, with no patient receiving more than two pairs, and with materials assigned at random within the pairs. Caries-free cervical erosion/abfraction lesions of the facial surface were restored without tooth preparation according to manufacturers' instructions, except that tooth structure to be restored was etched with 37% phosphoric acid prior to placement of Compoglass. Restorations were clinically evaluated by two blinded examiners at baseline, 6 months, and 1 year, using modified Ryge/USPHS criteria. Restorations receiving a score of "Charlie" in either retention or secondary caries were classified as failed restorations. The incidence of failures was statistically analyzed as a pairwise comparison, using an exact binomial test. RESULTS: Thirty-one pairs of restorations were available for recall at 1 year. The percentage of Alfa scores for each material in each category were: Retention (C = 84%, F = 100%), Color match (C = 81%, F = 100%), Marginal discoloration (C = 78%, F = 97%), Secondary caries (C = 88%, F = 100%), Anatomic form (C = 92%, F = 100%), and Marginal adaptation (C = 26%, F = 46%). Except for the failed restorations, no other Charlie scores were assigned. A significant difference in the incidence of failed restorations was found between the materials (P = 0.01).

Adult↗
PubMed2006

[The effects of remain of residual tooth on retention of post-core crown system].

This study was aimed to assess the effects of remain of residual tooth on the retention of postpost-core was made,casted and cemented. The post-core was tested at the speed of 10 mm/min on the Instron4302, and the retention force was recorded. Other samples were made and subjected to the test for cohesion of polymethylmethacrylate and metal. The result showed that retention significantly increased with the adding of the residual tooth. When the length of post was longer than 8 mm and 1 mm was added to tooth remain, the difference in retention between the two groups was statistically significant. It was noted that there existed relationships of retention to length of post and tooth remain, of cohesion to length of post and tooth remain, and of frictiion resistence to length of post and tooth remain; moreover, the relevant linear regression equations were obtained. So during the tooth preparation of post-core system, the tooth tissue should be reserved as much as possible.

Crowns↗
PubMedDate not supplied

Wettability of nonaqueous elastomeric impression materials.

The wettability of eight nonaqueous elastomeric impression materials was studied by comparing their contact angles. The materials included three polyethers (one of which was light activated), three hydrophilic poly(vinyl siloxanes), one conventional poly(vinyl siloxane), and one poly(vinyl siloxane) putty. Extracted teeth were prepared to approximate the roughness of a tooth preparation. Contact angles were measured at different time intervals after the start of mixing but were not shown to be significant. The nonhydrophilic poly(vinyl siloxane) materials and the poly(vinyl siloxane) putty were found to be significantly less wettable.

Analysis of Variance↗
PubMed1993

Autogenous tooth transplantation: a reevaluation.

This paper discusses whether autogenous tooth transplantation can survive as an option in the future dental armamentaria. Clinically, successful transplants must show a radiolucent space between the roots and surrounding bone. There must be no evidence of ankylosis, no permanent root resorption, and no inflammation. Histologically, the criterion of success is a normal and functional periodontal ligament between the root surfaces of transplants and the bone or gingival connective tissues. Case reports are presented to illustrate replantation or transplantation of teeth. Possible donor teeth are those with the proper amount of viable periodontal ligament, single-rooted teeth, third molars, and malpositioned or impacted teeth. The transplantation procedure involves extraction of the donor tooth, measurement of the root form and amount of periodontal ligament, preservation of donor tooth, preparation of recipient socket, positioning of donor tooth, suturing, and temporary splinting.

Adolescent↗