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PubMed2001

An in vitro study into the effect of the ferrule preparation on the fracture resistance of crowned teeth incorporating prefabricated post and composite core restorations.

AIM: This in vitro study investigated the effect of a ferrule preparation on the fracture resistance of crowned central incisors incorporating a prefabricated post (Parapost) cemented with Panavia-Ex and with a composite core. METHODOLOGY: The test group consisted of 10 post crowned natural central incisor teeth with a 2-mm wide ferrule preparation, whilst the control group of 10 teeth had no ferrule. The specimens were mounted on a Lloyd universal testing machine and a compressive load was applied at an angle of 135 degrees to the palatal surface of the crown until failure occurred. RESULTS: In both groups, failure occurred at higher loads compared with previous studies. The mean failure load was 1218 N for the unferruled group and 1407 N for the ferruled group. Statistical analysis showed no significant difference between the groups. CONCLUSIONS: Under the conditions of this study, when composite cement and core materials are utilized with a Parapost prefabricated system in vitro the additional use of a ferrule preparation has no benefit in terms of resistance to fracture.

Cementation↗
PubMed2006

Effect of enamel preparations on fracture resistance of composite resin buildup of fractures involving dentine in anterior bovine teeth: an in vitro study.

Sixty bovine teeth with simulated mesio-incisal angle fracture were randomly and equally divided in one untreated (control) group and three experimental groups (Bevel, Chamfer and newly introduced Stair-step Chamfer preparation group) to evaluate the effect of enamel preparations on the fracture resistance of composite resin. Post restoration, fracture mechanics approach was used to quantify the failure of composite resins in testing the samples in Instron testing machine. Mean peak failure load (Newton) of composite amongst experimental groups was observed in the order; Chamfer (326.09 +/- 72.73), Stair-step chamfer (315.21 +/- 81.77) and Bevel (253.83 +/- 67.38). Results of the One-Way ANOVA revealed significant difference in the mean peak failure load values of the four different groups. (P<0.001) Scheffe's Post-Hoc comparison test (Subset for alpha = 0.05) revealed that there was no significant difference in the mean peak failure load values of the bevel, stair-step chamfer and chamfer preparation when considered together, but the mean peak values of control group (605.22 +/- 48.96) were observed significantly higher. Failure mode evaluation revealed, majority of failures occurred as cohesive and mixed type for all the experimental groups. Adhesive type failure was observed maximum (33%) in the bevel group. Stair-step chamfer preparation showed greatest potential for application and use as it no only demonstrated comparable values to Chamfer preparation ['t' value (0.39) (P > 0.05)] but also involved sacrificing less amount of tooth structure adjacent to fractured edge.

Animals↗
PubMed2004

Computer-aided direct all-ceramic crowns: preliminary 1-year results of a prospective clinical study.

The objective of this study was to investigate the clinical performance of: (1) adhesively placed Cerec crowns with reduced stump preparations, and (2) Cerec endo crowns. The crowns were examined at baseline using modified USPHS criteria in 20 patients with 10 Cerec crowns with reduced stump preparations and 10 Cerec endo crowns. All crowns had been produced chairside with the Cerec 3 CAD/CAM method using the function mode. The crowns were machined from Vita Mk II feldspathic ceramic blocks, polished manually, and placed with dual-curing composite luting agent using a functional adhesive. After 1 year, a follow-up examination of the crowns was conducted; all 20 Cerec crowns were rated with a clinically acceptable A or B rating. Fractures or loss of retention were not observed. The method of producing and placing all-ceramic crowns with reduced stump preparations and endo crowns chairside in one appointment can be implemented successfully in private practice.

Adult↗
PubMedDate not supplied

An overview of esthetics with removable partial dentures.

A removable partial denture should restore function, phonetics, and esthetics. To assist the clinician in providing a restoration that is as esthetic as possible, despite the limitations of the conventional removable partial denture, this review collates the recommendations scattered among the literature. The review describes the steps involved in providing an esthetic restoration, including diagnosis and treatment planning; surveying; mouth preparation; framework and clasp alloys; clasps; rests; major connectors; minor connectors; prosthetic teeth; and denture base resin and flanges. The esthetic challenges of the Kennedy Class IV removable partial denture are also discussed.

Acrylic Resins↗
PubMed1999

[Ready-made crowns in the deciduous dentition].

The following review of the literature on "prefabricated crowns for deciduous teeth" attempts to highlight the benefits and limitations of this treatment modality. The use of prefabricated crowns is indicated in the following situations: severe destruction of the clinical crown, deep approximal cavities, bilateral approximal cavities, circumferential caries, history of root canal treatment, and need for fixed space retention. Compared to amalgam restorations involving two or more surfaces, prefabricated crowns on deciduous molar teeth gave very high survival rates. They consist of a chromium-nickel-steel alloy and are reported to have an acceptable gingival tolerance profile. In contrast to the Anglo-American countries this treatment modality is quite uncommon in Germany. A probable reason for this reservation could be that many clinicians often fail to see the need for a filling in the deciduous dentition. Besides, many dentists are reluctant to use local anesthesia in children, which is inevitable in preparing and fitting a prefabricated crown. In the United States and UK dentists are less frequently confronted with this problem, as complex treatments are often carried out under nitrous oxide sedation or insufflation anesthesia. Modern filling materials have been introduced which have the potential to narrow the indications for prefabricated stainless steel crowns. Against this background, future studies are necessary to compare the survival rates of prefabricated crowns and modern filling materials.

Child↗
PubMed2002

Effect of length and diameter of tapered posts on the retention.

The force transmission of tapered unthreaded posts along the root has been reported to be homogenous but their retentive strength was found to be lower compared with those of parallel unthreaded or other kinds of threaded posts. The purpose of this in vitro study was to investigate the effect of length and diameter on the retentive strength of sandblasted tapered prefabricated titanium posts (Erlangen post system). Posts with constant taper angle but with three different lengths (9, 12, 15 mm) and apical diameters (0.5, 0.9, 1.1 mm) were cemented using zinc phosphate cement into the prepared and roughened post spaces of 90 intact anterior teeth. The post retention concerning length and diameter, being independent from each other, was measured by a tensile force test. The retentive strength was found to be proportional to the length as well as to the diameter of the posts. The mean minimum strength (181 +/- 14 N) recorded for the thinnest and shortest post was significantly lower than that of mean maximum strength (612 +/- 85 N) obtained from those of the thickest and longest post. Proportional bond strengths of the posts comprising their surface areas ranged between 6.8 and 7.9 N mm(-2) which were not significantly different between any group. The retention was effected strongly with the increase in the length (approximately 100%) than with the increase in the diameter (approximately 60%). Concerning the posts tested in this study, it is concluded that some caution should be exercised in the choice of post with appropriate length rather than diameter for the tooth concerned.

Cementation↗
PubMed2005

In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations.

STATEMENT OF PROBLEM: The in vitro effectiveness of a uniform circumferential ferrule has been established in the literature; however, the effect of a nonuniform circumferential ferrule height on fracture resistance is unknown. PURPOSE: This in vitro study investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations. MATERIAL AND METHODS: Fifty extracted intact maxillary human central incisors were randomly assigned to 1 of 5 groups: CRN, no root canal treatment (RCT), restored with a crown; RCT/CRN, no dowel/core, restored with a crown; 2 FRL, 2-mm ferrule, cast dowel/core and crown; 0.5/2 FRL, nonuniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast dowel/core and crown; and 0 FRL, no ferrule, cast dowel/core and crown. The teeth were prepared to standardized specifications and stored for 72 hours in 100% humidity prior to testing. Testing was conducted with a universal testing machine with the application of a static load, and the load (N) at failure was recorded. Statistical analysis was performed with a 1-way analysis of variance and the Tukey Honestly Significant Difference test (alpha=.05). The mode of fracture was noted by visual inspection for all specimens. RESULTS: There was strong evidence of group differences in mean fracture strength ( P <.0001). Following adjustment for all pairwise group comparisons, it was found that the lack of a ferrule resulted in a significantly lower mean fracture strength (0 FRL: 264.93 +/- 78.33 N) relative to all other groups. The presence of a nonuniform (0.5 to 2-mm vertical height) ferrule (0.5/2 FRL: 426.64 +/- 88.33 N) resulted in a significant decrease ( P =.0001) in mean fracture strength when compared with the uniform 2-mm vertical ferrule (2 FRL: 587.23 +/- 110.25 N), the group without RCT (CRN: 583.67 +/- 86.09 N), and the RCT-treated tooth with a crown alone (CRN/RCT: 571.04 +/- 154.86 N). The predominant mode of failure was an oblique fracture extending from the lingual margin to the facial surface just below the insertion of the tooth into the acrylic resin. CONCLUSION: The results demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.

Crowns↗
PubMedDate not supplied

Microleakage of cements for stainless steel crowns.

Microleakage is related to recurrent decay, inflammation of vital pulps, and reinfection of previously treated root canals. The purpose of this investigation was to compare the abilities of new adhesive cements and conventional nonadhesive controls to prevent microleakage under stainless steel crowns on primary anterior teeth. Standardized preparations were made, and stainless steel crowns were adapted. Specimens were assigned randomly to cement groups: zinc phosphate (ZP), polycarboxylate (PC), glass-ionomer (GI), resin-modified glass-ionomer (RMGI), RMGI with a dentin bonding agent (RMGI + DBA), adhesive composite resin (ACR) and zinc oxide eugenol (ZOE). Specimens were stored in water, aged artificially, stained, embedded, and sectioned, and the microleakage was measured. Group means and standard errors were calculated. ANOVA discerned differences among groups (P < 0.0001), and Turkey's multiple comparisons testing (P < 0.05) ranked the groups from least to most microleakage as follows: [RMGI + DBA, RMGI, ACR, GI], [ZP], and [PC, ZOE]. The adhesive cements significantly reduced microleakage.

Adhesives↗
PubMed1997

Development of a novel system for assessing tooth and restoration wear.

OBJECTIVES: This investigation sought to develop a mapping apparatus for use in the assessment of both tooth and restoration wear. METHODS: A computer controlled mapping device, capable of scanning a suitably prepared electroconductive tooth replica by means of an electrical feedback mechanism, was constructed and its accuracy assessed by measuring the thicknesses of four engineers' slip gauges 12 times each. The reproducibility of three potential methods of rendering a die stone replica electroconductive was also investigated. Finally, tooth replicas were surface profiled and compared empirically with the originals using a commercial surface mapping program. RESULTS: The overall mean accuracy of the mean thicknesses of the slip gauges was 4.4 (2.8) microns. Surface deposition of either nickel spray or gold leaf, upon a ready formed replica, did not give a reproducible thickness. Precoating silicone impressions with nickel spray prior to replica production overcame this problem. On an empirical basis the instrument yielded accurate digital terrain models of tooth replicas. CONCLUSIONS: A surface mapping device has been developed which is both accurate and reproducible. A satisfactory electroconductive surface may be produced upon a tooth replica by precoating a silicone impression with nickel spray before casting the replica. The technique should prove invaluable for monitoring both tooth and restoration wear but further work is necessary to examine how such an approach will perform clinically.

Dental Impression Materials↗
PubMed2000

Adapting crown preparations to adhesive materials.

Traditional approaches to crown preparation for replacement crowns or teeth with short clinical crowns are often overly destructive of tooth tissue. Adhesive cements or composites combined with dentine bonding agents provide the clinician with some flexibility in treatment planning and should be considered when more destructive techniques would otherwise be necessary.

Adhesives↗
PubMed2000

A simple and cost-effective method for preparing DNA from the hard tooth tissue, and its use in polymerase chain reaction amplification of amelogenin gene segment for sex determination in an Indian population.

The use of teeth as an important resource in the analysis of forensic case history by polymerase chain reaction (PCR) or other related methods has been reported. However, a major drawback in using teeth has been that the DNA is present only in trace amounts, and the methods to recover DNA from the flinty material have not been efficient or cost effective. In this report, we describe a method to prepare DNA from the hard tooth tissues. Our studies show that ultrasonication of teeth samples yields sufficient amounts of good quality DNA useful for PCR-based diagnostic methods. The teeth could serve as a reliable source of DNA for amplification-based forensic methods in sex determination. DNA could be obtained from any tooth, regardless of the age of subject. Furthermore, by using the AMEL gene-based primers in PCR, we have shown that the AMEL gene serves as a good marker for sex determination in the Indian population. In our study, the PCR-based method was sensitive and proved to be successful for sex determination with a complete specificity.

Adolescent↗
PubMedDate not supplied

Retention of veneered stainless steel crowns on replicated typodont primary incisors: an in vitro study.

PURPOSE: The purpose of this in vitro study was to determine the effect of crimping and cementation on retention of veneered stainless steel crowns. METHODS: One hundred twenty crowns, 90 from 3 commercially available brands of veneered stainless steel crowns (Dura Crown, Kinder Krown, and NuSmile Primary Crown) and 30 (plain) Unitek stainless steel crowns were assessed for retention. An orthodontic wire was soldered perpendicular to the incisal edge of the crowns; the crowns were fitted to acrylic replicas of ideal crown preparations and were divided equally into 3 test groups: group 1--crowns were crimped only (no cement used); group 2--crowns were cemented only; and group 3--crowns were crimped and cemented to the acrylic replicas. An Instron machine recorded the amount of force necessary to dislodge the crowns and the results were statistically analyzed using 2-way ANOVA and Tukey honestly significant difference (HSD) test. RESULTS: Group 3 was statistically more retentive than groups 1 and 2. Group 2 was statistically more retentive than group 1 (P < .001). In group 1, Unitek crowns were statistically more retentive than the veneered crowns (P < .05). In group 2, NuSmile crowns showed statistically less retention values than all other crowns (P < .05). In group 3,Kinder Krown crowns showed statistically better retention rates than all other brands (P < .05). CONCLUSIONS: Significantly higher retention values were obtained for all brands tested when crimping and cement were combined. The crowns with veneer facings were significantly more retentive than the nonveneered ones when cement and crimping were combined.

Analysis of Variance↗
PubMed1998

Effects of repeated hand instrumentation on the marginal portion of a cast gold crown.

A study was conducted to evaluate the effects of repeated hand instrumentation on the marginal portion of a cast gold crown. Seven extracted periodontally diseased premolars were used. The finishing line of the preparation was placed on the root surface and then the crown was cast and cemented in the usual manner. One proximal surface of each sample was divided into 2 areas: root planing (RP) area and RP plus polishing (RPP) area. The marginal portion of the crown was measured to give a baseline value using a surface roughness- and profile-analyzing system. Then, the marginal portion was painted with a waterproof pen. RP was performed to remove paint in the RP area with the curets. In the RPP area, RP followed by polishing was done by silicone polishing points and a rubber cup with polishing paste. The relevant procedures and measurements were repeated 3 times in each area. Changes in the sample roughness and profile were evaluated and compared between the 2 techniques. The results showed that repeated instrumentation altered the surface of the marginal portion of the cast gold crown, resulting in increased roughness in both areas (P < 0.01). However, the roughness of the RPP area was considerably restored to the baseline value by polishing after RP. Therefore, it is suggested that polishing after RP smoothes the marginal portion of the cast gold crowns and appears to be an efficient prophylactic system.

Bicuspid↗
PubMed2004

Effect of margin location on crown preparation resistance form.

STATEMENT OF THE PROBLEM: The location of preparation margins may compromise the fixed prosthodontic restoration's resistance form. Purpose This study evaluated changes of opposite wall margin position on rotational resistance form compared to the equal-height margin configuration. MATERIAL AND METHODS: The trigonometric computation of the minimal resistance form preparation taper, alpha1 , was determined using a previously described formula. The alpha1-values for different tooth sizes with variation of base widths (range 4 to 10 mm) and vertical wall heights (range 4 to 9 mm) were calculated. The alpha1-values represent resistance form with both opposing wall margins at the same vertical height position. The alpha2-values were calculated with additional formulas to address uneven margin heights. Calculated alpha2-values of 10 degrees or less were considered clinically significant due to the known level of difficulty for the clinician. RESULTS: As a general trend, the alpha2-values were reduced compared to the alpha1-values with shortening opposing vertical wall heights in all tooth-size categories. Clinically significant changes in the resistance form taper were shown in all tooth size categories except the smallest 4-mm tooth base size. CONCLUSION: Fixed prosthodontic restoration resistance form is negatively affected by uneven vertical margin placement. This phenomenon reduces the resistance form of the restoration compared to equal-height margin placement.

Crowns↗
PubMed1996

Effect of dowel lubrication on resistance to dislodgment of dowels cemented with a 4-META resinous cement.

Dentatus stainless steel dowels were cemented 5 mm into prepared canals of extracted human teeth with C&B Metabond cement. One half the dowels were lubricated before cementation to ensure easy subsequent retrieval. Significantly less tensile force was required to dislodge the lubricated dowels (p = 0.0209). Retrievable lubricated dowels could provide dentists the option of nonsurgical endodontic retreatment in lieu of endodontic surgery. However, lubrication cannot be recommended for clinical use at this time because of the potential for the dowel to unscrew during normal oral function. Further studies are required to determine the effects of rotational forces on the lubricated dowel, surface design of the dowel on retention, and chemical interaction of the lubricant on the resinous cement. Long-term effects of the lubricant on the cement are unknown.

Acrylic Resins↗