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PubMed2004

Effect of finish line variants on marginal accuracy and fracture strength of ceramic optimized polymer/fiber-reinforced composite crowns.

STATEMENT OF PROBLEM: Ceramic optimized polymer (Ceromer)/fiber-reinforced composite (FRC) crowns have been promoted as alternatives to conventional crowns. However, little is known regarding the ideal tooth preparation for this type of crown. PURPOSE: This in vitro study evaluated the marginal adaptation and fracture strength of ceromer/FRC crowns with respect to the various types of finish lines. MATERIAL AND METHODS: Four metal dies with different finish lines (0.9-mm chamfer, 1.2-mm chamfer, 1.2-mm rounded shoulder, and 1.2-mm shoulder) were prepared. Forty (10 for each finish line) Targis/Vectris crowns were fabricated on duplicated base metal alloy dies. The restorations were stereoscopically evaluated at 56 points along the entire circumferential margin for measuring the margin adaptation before and after cementation with a resin luting agent. The specimens were then compressively loaded to failure using a universal testing machine. The marginal adaptation (microm) was analyzed with the Kruskal-Wallis test and post-hoc Dunnett test (alpha=.05). The fracture load (N) was analyzed with a 1-way analysis of the variance and the Scheffe adjustment (alpha=.05). The fractured surfaces of the crowns were examined with a scanning electron microscope to determine the mode of fracture. RESULTS: The marginal adaptation of crowns with a shoulder finish line was significantly better than crowns with a chamfer finish line before and after cementation (P<.001). The increased marginal gap after cementation was the lowest in the 1.2-mm rounded shoulder group. The fracture strength of the crowns with the 0.9-mm chamfer and crowns with 1.2-mm chamfer was significantly greater than those of the crowns with the 1.2-mm shoulder or rounded shoulder (P=.011, P=.049, respectively). The mean fracture load of all crowns, regardless of the finish line design, was 1646 N. The fractured surface of the crown revealed adhesive failure and 3 types of cohesive failure (fracture of the Targis and Vectris, Targis fracture with a crack in the Vectris layer, and crushing without fracture). CONCLUSION: The marginal gaps were greater for the chamfer finish line specimens than in the shoulder finish line specimens. However, the fracture strength of the chamfer finish line specimens was greater than that of the shoulder finish line specimens.

Analysis of Variance↗
PubMed2006

Complications associated with fixed partial dentures with a loose retainer.

STATEMENT OF PROBLEM: When 1 retainer of a definitive fixed partial denture (FPD) becomes loose, the clinician has the option of either sectioning and removing the FPD or attempting removal of the intact cemented retainer. Excessive force during attempted FPD removal may irreversibly damage dentition. PURPOSE: This study evaluated the type and frequency of complications that may accompany the removal of definitive cemented FPDs with a single loose retainer. MATERIAL AND METHODS: Participants included 22 patients with a definitive cemented FPD with complete cast crown coverage castings in which 1 retainer became loose and the other retainer remained cemented. Cemented FPD retainers were removed using 1 of 2 attachments supplied with a crown removal system (Dentco). The patient and FPD characteristics, type of attachment, number of attempts before removal, condition of removed FPD, and condition of the abutment teeth were recorded. Descriptive statistics were used to analyze the data. RESULTS: Clinical findings recorded prior to FPD removal showed that 41% of patients were unaware they had a loose FPD retainer and 82% reported no discomfort associated with the loose retainer. Caries were noted on 50% of the teeth with a loose retainer. Damage resulting from attempted removal of the cemented retainer included minor porcelain fracture (9%), minor core chipping (14%), minor incisal edge chipping of tooth preparations (27%), and major damage to the abutment tooth (4%). CONCLUSION: Retrieval of an intact FPD and recementation was possible 64% of the time.

Adult↗
PubMed2000

Restoration of extensive erosion areas using an indirect composite technique.

Cervical erosion defects, particularly those of extensive size that are located in an area where control of the operative field is difficult, can present a significant restorative challenge. This article describes an indirect restorative technique to solve this problem. Following tooth preparation, an indirect restoration is luted to the tooth and the margins are finished and polished. Using an indirect technique minimizes operative field isolation time and the total chairside time required to restore the tooth. Clinical cases are presented to illustrate this technique.

Adult↗
PubMed1990

[Spectroscopically controlled preparation of hard tooth structures using a UV laser].

During preparation of hard tooth structures with a 193nm-(ArF)*-excimer laser, the laser beam produces a specific fluorescent light whose spectrum is governed by the structure of the specimen. These fluorescence spectra allow an analysis of the removed tissues. The data thus obtained may be used to control the laser system so that only specific structures, such as carious tissue, are removed: reproducible fluorescence spectra were established by means of standardized samples (pure synthetic hydroxyl apatite ceramics, enamel, dentine and carious dentine) and the characteristic absorption bands (peaks) for the different substances were measured. With the aid of electronic data processing these reference spectra could be compared with the fluorescence spectra obtained during preparation. When a spectrum differed from the predefined limits of relative intensities, preparation was stopped. Since ablation per pulse is only to a small depth (0.04-4 microns) with the 193nm-(ArF)*-eximer laser, this feedback system of ablation and fluorescence spectroscopy allows decisions as to continuing or stopping the preparation process to be taken within the range of a few microns.

Dental Cavity Preparation↗
PubMed1991

Temperature change in the pulp chamber during complete crown preparation.

This study observed the temperature changes in the pulp chamber during tooth preparation for a complete crown. Twelve extracted, morphologically intact human teeth were chosen: four canines, four premolars, and four molars. Six teeth, two of each, were cooled during preparation with an air-water spray; the remaining six were air-cooled. Minimal reduction of dentin using an air-water spray coolant resulted in a lowered temperature in the pulp chamber, mainly with the cross-grooved TDA diamond stones. The application of an air coolant resulted in a temperature rise in the pulp chamber.

Air↗
PubMed1999

Porcelain veneers bonded to tooth structure: an ultra-morphological FE-SEM examination of the adhesive interface.

OBJECTIVES: The porcelain veneer technique bonds a thin porcelain shell to a minimally prepared tooth surface (enamel and/or dentin) with a luting composite in combination with an adhesive system. When complete, two adhesive interfaces are formed--resin to etched porcelain and resin to tooth structure. The purpose of this laboratory investigation is to analyze the ultra-structure of these two adhesive interfaces in order to find an explanation for some clinical phenomena and/or shortcomings of bonded porcelain veneers. METHODS: The surfaces of four porcelain disks were treated successively by sandblasting, etching with hydrofluoric acid, ultrasonic cleaning, and silanizing. The effect of each step on the surface structure of the porcelain was evaluated by field-emission scanning electron microscopy (FE-SEM). In addition, the effect of acid etching the tooth surface of veneer preparations on seven extracted upper anterior teeth was similarly determined. Finally, pre-treated porcelain veneers were luted to veneer preparations on 12 extracted upper anterior teeth by means of a contemporary total-etch adhesive system and a photo-polymerizable luting composite. The tooth/luting composite and the luting composite/porcelain interface of the veneer complex were then evaluated ultra-morphologically by FE-SEM after the specimens had been etched with an argon-ion beam to enhance the surface relief. RESULTS: FE-SEM imaging of the tooth/luting composite/porcelain interface showed strong micro-mechanical interlocking of the luting composite in the micro-retentive pits both of the acid-etched tooth surface and in the etch pits of the acid-etched porcelain surface. From this ultra-morphological perspective, the etched porcelain surface is more retentive than the etched tooth surface. At the tooth surface, cervical aprismatic enamel and exposed dentin showed the least resin-receptive surface texture. However, in these areas, no separation of the interface was observed when a multi-step total-etch adhesive system was used. SIGNIFICANCE: The strong interlocking of the luting composite into the retentive etch pits of both the porcelain and tooth substrates contributes to strong adhesion of porcelain veneers with good retention. This study suggests that a modern multi-step total-etch adhesive system can produce adhesion even to the less retentive cervical enamel and exposed dentin. Further clinical research is necessary to evaluate the long-term retention of porcelain veneers and to correlate these in vitro observations with clinical performance.

Acid Etching, Dental↗
PubMed1990

Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. 2. Cavosurface bonding and cavosurface plus internal enamel bonding.

The purpose of this study was to test the difference between the strength of the marginal ridge of extracted teeth with a Class I composite resin restoration and the strength of the marginal ridge of teeth with a Class II amalgam restoration with retention grooves. A statistically significant difference in fracture strengths was found among groups. No statistically significant difference was found among restored preparations, beveling technique, and restorative material. Statistically significant differences in fracture strength were found between the whole tooth group and treatment groups; between the whole tooth group and Class II amalgam restoration group; and between the unrestored tooth preparation group and all other tooth groups.

Acid Etching, Dental↗
PubMed1995

Scanning electron micrographic effects of air-abrasion cavity preparation on human enamel and dentin.

Recent developments in technology and restorative materials have renewed interest in air abrasion as a means of tooth preparation. The technique, also called kinetic cavity preparation, uses kinetic energy to remove tooth structure. The purpose of this investigation was to use scanning electron microscopy to compare the effects of this technique to those of high-speed burs on extracted human teeth. Class V buccal preparations were made on five teeth with a No. 34 carbide bur used at 400,000 rpm and on 23 teeth with kinetic cavity preparation using differing combinations of aluminum oxide particle sizes and delivery pressures. Features of the specimens prepared at high speed included sharp line angles, chipping of the cavo-surface margin, and striated internal surfaces. Kinetic cavity preparations had rounded cavo-surface margins and internal line angles. The surfaces were microscopically rough and the dentinal tubules were occluded. There was little difference in appearance between specimens treated with various combinations of particle sizes and delivery pressures.

Air Pressure↗
PubMed1995

[Morphological changes in the periodontium from the use of different designs of metal ceramic dentures].

Morphological changes in the periodontium during the use of cermet crowns of different design were studied in experimental animals. The status of the periodontium was found to depend on the level of crown fixation with respect to gingival edge. Histological findings had show that position of a cermet crown at the level of the gingival edge does not involve appreciable changes in the periodontium, though preparation of abutment teeth with the formation of a step be considered as preferable. A subgingival position of cermet crowns leads to development of an inflammatory reaction in the periodontium, the severity of this reaction being related to a great measure to the method of the tooth preparation. If a step is formed during preparation of a tooth, the inflammatory changes are less pronounced than when there is no step formed. In the latter case the pathological changes were seen in the periodontium. The authors come to a conclusion that cermet crowns should be fixed at the level of the gingival edge. When making cermet crowns, abutment teeth should be prepared with the formation of a pericervical step.

Animals↗
PubMedDate not supplied

Effect of thickness of flowable resins on marginal leakage in class II composite restorations.

Despite limited scientific evaluation, there is an increased use of low elastic modulus flowable resin composite (FRC) as a stress-relieving gingival increment in Class II restorations. This study compared marginal leakage in preparations with gingival margins in enamel or dentin/cementum (sub-CEJ and supra-CEJ) after FRC was used as a gingival increment to hybrid resin composite used alone. In addition, the extent of leakage around restorations with or without the use of FRC gingival increments when light curing the resin composites from occlusal direction only or buccal, lingual and occlusal directions was compared. Sixty extracted human molars were prepared with two identical Class II (MO and OD) preparations (30 were 1 mm sub-CEJ and 30 were 1 mm supra-CEJ) and randomly assigned to six groups. After etching, dentin-bonding agent was applied to all prepared tooth surfaces according to the manufacturer's specifications. One of three different thicknesses of FRC (0.5 mm, 1 mm or 2 mm) was placed on the gingival floor, cured and a hybrid resin composite was placed occlusally to complete the restoration. The control preparation on each tooth was restored in the same manner, except that a hybrid resin composite was used for both the gingival and occlusal increments. The restored teeth were thermocycled (300 cycles), then immersed in 50% silver nitrate prior to the hemi-section and measured for leakage under a light microscope. The data were evaluated using paired measures analysis of variance (ANOVA). Most of the occlusal margins showed no leakage, while almost every gingival margin demonstrated some silver nitrate penetration regardless of whether it was located sub or supra-CEJ, although significantly less leakage was found in restorations with supra-CEJ margins (p=0.0001). Among supra-CEJ restorations, there was a pronounced reduction in leakage as FRC thickness increased (p=0.0005). In the teeth restored with the gingival-margin located supra-CEJ, the 2 mm thickness FRC gingival increment showed significantly less leakage (p<0.01) compared with the 0.5 mm thickness of FRC gingival increment. The direction of the curing light did not affect the extent of leakage (p>0.05). The use of FRC material as a gingival increment sub-CEJ in posterior hybrid resin restorations produced no significant difference in leakage (p>0.05). The results of this study indicated that restorations located supra-CEJ (with gingival margins in enamel) with 2 mm thick FRC gingival increments demonstrated significantly less leakage than did those with 0.5 mm FRC. When the margin of the restoration was located sub-CEJ (in dentin/cementum), neither the thickness nor the presence of FRC as a gingival increment significantly influenced the marginal leakage.

Acid Etching, Dental↗
PubMed2002

A retrospective study of pulpal response in vital adult teeth prepared for complete coverage restorations at ultrahigh speed using only air coolant.

STATEMENT OF PROBLEM: The dental literature has shown a 3% to 25% pulpal necrosis rate as a result of tooth preparation for complete coverage restorations. PURPOSE: The purpose of this retrospective study was to examine clinical and radiographic records for evidence of pulpal necrosis in teeth prepared for complete coverage restorations at ultrahigh speed when air coolant alone was used. MATERIAL AND METHODS: The 1847 teeth in this study (182 fixed partial denture abutment teeth and 1665 single teeth restored with 21 all-ceramic, 1095 metal-ceramic, and 731 all-metal restorations) were prepared with diamond instruments (burs) in a sweeping or painting motion with the use of light pressure (1-3 oz) at ultrahigh speed with air coolant alone from the handpiece. New burs were used for each patient and then discarded. Each bur was used on no more than 4 teeth. All impressions were made with reversible hydrocolloid. Provisional restorations were fabricated on a stone cast and cemented with zinc oxide and eugenol cement. Provisional restorations were removed at 3 to 4 weeks and definitive restorations placed. Between 1970 and 1989, 6 different luting agents (zinc phosphate, resin, glass ionomer, ortho-ethoxybenzoic acid, carboxylate, and polycarboxylate) were used to place definitive restorations. All patients were questioned about symptoms of tooth sensitivity, tenderness, or pain at their regular (4- to 6-month) hygiene recall appointments. Success was defined as any definitively restored teeth that remained free of radiographic evidence of periapical radiolucency and clinical signs and symptoms of pulpal sensitivity or pain recorded in the clinical record. The results were compared with rates of pulpal necrosis for teeth prepared with water coolant as reported in the dental literature published between 1970 and 1997. RESULTS: Of 638 teeth prepared between 1970 and 1979, the pulpal necrosis rate was 2.19% (14 teeth: 12 single teeth and 2 fixed partial denture abutment teeth) (97.81% success rate). Of 1209 teeth prepared between 1980 and 1989, the pulpal necrosis rate was 0.66% (8 teeth: 7 single crown teeth and 1 partial denture abutment tooth) (99.34% success rate). Of 1825 teeth prepared between 1970 and 1989, radiographic evidence of pulpal necrosis was found in 0% (100% success rate). No clinical symptoms of pain or sensitivity were recorded in the patient records for the surviving teeth during the time period of this study, which was conducted in May 2001. No crowns were repaired or removed as a result of carious lesions. No higher incidence of pulpal necrosis relative to the type of luting agent was observed. CONCLUSION: Within the limitations of this retrospective study, it is suggested that tooth reduction procedures can be completed with minimal damage to the pulp when only air coolant from the dental handpiece is used.

Adult↗
PubMed1992

[The form of retention and resistance of dental preparations. A review of the literature and the clinical implications].

Generally, the principles of tooth preparation are well established in the majority of textbooks dealing with fixed prosthodontics. However, one specific related aspect, retention and resistance form, still features some elements that might be less known to the clinician. The purpose of the present literature review is to contribute to the classification and current understanding of the terms of retention and resistance. Finally, the resulting clinical implications, focusing primarily on cast full veneer and porcelain-fused-to-metal crowns, will be discussed.

Bite Force↗
PubMed1985

Rationale for designing cavity preparations.

Increased resistance to caries, increased dental awareness, superior diagnostic capabilities, better illumination, optical aids that significantly enhance vision, improved and standardized materials for restoration, and a deeper understanding of the caries process enable a far more conservative approach to tooth preparation. The dentist can concentrate on preserving as much sound tooth structure as possible with less attention being devoted to resistance and retention form that previously demanded in bulk restorations and massive channels and locks that are no longer appropriate. Although caries inhibitory effects have been shown with materials such as silicate cement, glass ionomers, and resins that leach fluoride, in general, dentists should not rely on restorative materials to inhibit the development of future decay. Characteristics of the carious lesion are unique for each tooth according to many factors centering around the plaque pattern for that tooth and not according to zones of natural susceptibility or immunity strictly dictated by morphology. Therefore, no single cavity preparation duplicated from a textbook is likely to be satisfactory for an individual tooth. Furthermore, novices learning the subject of cavity preparation often leave decalcified enamel when they attempt to replicate under clinical conditions that which they have learned in technique courses. This is the major invitation to future caries reappearing adjacent to restorations. Also, failure to duplicate the exact morphology of the tooth surface that has been replaced is likely to alter the pattern of plaque accumulation and create other caries prone areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Composite Resins↗
PubMed1996

Dual-arch impressions as a diagnostic aid--a case report.

This article describes dual-arch impression technique (DAIT) used with alginate impression material, to obtain diagnostic models of the prepared and opposing teeth. Using this quick and simple procedure, tooth preparation, abutment parallelism, and occlusal clearance can all be critically assessed outside the mouth. Any problem areas can be corrected at a subsequent appointment, prior to taking the final impression.

Alginates↗
PubMed1999

Intracrown ring for crown and fixed partial denture abutments.

When a tooth prepared for a crown does not comply with the general principles of retention and resistance form, and it is not possible to correct it without damage to the biologic structures of the tooth, consideration must be given to the purpose of the crown, such as whether it is a single crown, a retainer for a fixed restoration, or a retainer for a fixed removable prosthesis with precision attachments. The crown prepared with receptacles for internal attachments will undoubtedly require more retention and resistance to dislodgment than a single crown because of forces that will be applied to it through the removable portion of the restoration. The purpose of this article is to present an alternative procedure that uses the intracrown ring, which provides additional retention for the abutment crown because of the compressible ring. The compressible ring is placed in the groove prepared in the lower third of the abutment during the crown preparation.

Crowns↗
PubMed2005

Immediate dentin sealing improves bond strength of indirect restorations.

STATEMENT OF PROBLEM: Delayed dentin sealing is traditionally performed with indirect restorations. With this technique, dentin is sealed after the provisional phase at the cementation appointment. It was demonstrated that this chronology does not provide optimal conditions for bonding procedures. Immediate dentin sealing (IDS) is a new approach in which dentin is sealed immediately following tooth preparation, before making the impression. PURPOSE: The purpose of this study was to determine whether there were differences in microtensile bond strength to human dentin using IDS technique compared to delayed dentin sealing (DDS). MATERIAL AND METHODS: Fifteen freshly extracted human molars were obtained and divided into 3 groups of 5 teeth. A 3-step etch-and-rinse dentin bonding agent (DBA) (OptiBond FL) was used for all groups. The control (C) specimens were prepared using a direct immediate bonding technique. The DDS specimens were prepared using an indirect approach with DDS. Preparation of the IDS specimens also used an indirect approach with IDS immediately following preparation. All teeth were prepared for a nontrimming microtensile bond strength test. Specimens were stored in water for 24 hours. Eleven beams (0.9 x 0.9 x 11 mm) from each tooth were selected for testing. Bond strength data (MPa) were analyzed with a Kruskal-Wallis test, and post hoc comparison was done using the Mann-Whitney U test (alpha=.05). Specimens were also evaluated for mode of fracture using scanning electron microscope (SEM) analysis. RESULTS: The mean microtensile bond strengths of C and IDS groups were not statistically different from one another at 55.06 and 58.25 MPa, respectively. The bond strength for DDS specimens, at 11.58 MPa, was statistically different (P=.0081) from the other 2 groups. Microscopic evaluation of failure modes indicated that most failures in the DDS group were interfacial, whereas failures in the C and IDS groups were both cohesive and interfacial. SEM analysis indicated that for C and IDS specimens, failure was mixed within the adhesive and cohesively failed dentin. For DDS specimens, failure was generally at the top of the hybrid layer in the adhesive. SEM analysis of intact slabs demonstrated a well-organized hybrid layer 3 to 5 microm thick for the C and IDS groups. For DDS specimens the hybrid layer presented a marked disruption with the overlying resin. CONCLUSIONS: When preparing teeth for indirect bonded restorations, IDS with a 3-step etch-and-rinse filled DBA, prior to impression making, results in improved microtensile bond strength compared to DDS. This technique also eliminates any concerns regarding the film thickness of the dentin sealant.

Dental Bonding↗
PubMed1999

Evidence that laminin-5 is a component of the tooth surface internal basal lamina, supporting epithelial cell adhesion.

Laminin-5 (Ln-5) is an extracellular matrix (ECM) glycoprotein found in epithelial basal laminae. We studied its expression on the surface of rat molars, in relationship to the location of the internal basal lamina (IBL) of the junctional epithelium (JE). In order to avoid disruption of the JE-tooth interface as much as possible, the surface of molars was prepared by mechanical removal of tissue debris and detergent/osmotic lysis of epithelial cell layers, and directly stained by immunohistochemistry, without sectioning. Antibodies to Ln-5 specifically stained a narrow band in the region of the cemento-enamel junction (CEJ), consistent with the expected location of the IBL. Western blotting of ECM material detergent--solubilized from the prepared tooth surfaces confirmed the molecular nature of Ln-5 identified by immunohistochemistry. By the use of a high-definition 3-D microscope, it appeared that Ln-5 coated the most apical part of the enamel and the most coronal portion of the cementum, on either side of the CEJ. In adhesion assays performed directly on tooth surfaces, epithelial cells adhered preferentially to the Ln-5 coated area of the tooth compared to the root surface, which is coated by other ECM components. Adhesion to the Ln-5 coated surface was specifically inhibited by a function-blocking monoclonal antibody to Ln-5. These results suggest that Ln-5 is a component of the IBL, and that it may be important in promoting adhesion of JE cells onto the tooth surface.

Animals↗