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PubMed1989

[Step-back method for intracanal preparation with multiple length determination of the tooth root canal].

A procedure of intracanal preparation of a cuneiform with cervical extension using a step-back technique is described. The length of the root canal is determined by multiple electric measurement. First, the initial measurement of the canal length (I1) is performed. The measured length is then transferred to the initial extender (No. 15), whereafter extirpation of the pulp and removal of circumpulpal dentin begin. Then the extender NO. 20 is reduced by 1 mm, and the extender No. 25 by 2 mm. When the canal have been narrowed and bent, further extenders are used to additionally reduce the working length by 1 mm more. When the pulp has been extirpated, the second canal length measurement (12) is performed, then starting to form the canal. In phase 1, the apical third from the initial (IAF) to the leading file (MAF) is treated and the cervical extension of the canal prepared by a bur drill. In further instrumentation, each next file is reduced by 1 mm of the measured canal length (12), thus shaping the canal by filling, using a step-back method. Files according to Hedström should be used thereby. Shaping of the canal is completed by a file by four numbers greater than the leading (MAF) one.

Dental Pulp Cavity↗
PubMed1997

Influence of tooth surface roughness and type of cement on retention of complete cast crowns.

STATEMENT OF PROBLEM: Bond strength of luting cements to dentin is a critical consideration for success of cast restorations. PURPOSE OF STUDY: This study determined the relationship between surface characteristics of teeth prepared for complete cast crowns and retention of respective cemented restorations. MATERIAL AND METHODS: Ninety artificial crowns were cast for standardized complete crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Diamond, tungsten carbide finishing, and cross-cut carbide burs of similar shape were used. The crowns in each group were randomly subdivided into three subgroups of 10 for the three luting cements selected for this study: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia-EX). Retention was evaluated by measuring the tensile load required to dislodge the artificial crowns from tooth preparations with an Instron testing machine. RESULTS: Analysis of forces with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both luting cement and finishing burs (p < 0.001). A statistically significant interaction effect (p < 0.001) was also found. The greatest retention value (372.9 N) was for tooth preparations refined with carbide burs and cemented with Panavia-EX cement. However, the least retention value (201.6 N) was for tooth preparations completed with finishing burs and luted with zinc phosphate cement. CONCLUSIONS: Significant differences were found among all three cements for finishing burs. However, there was a difference only between Panavia-EX cement and the other two cements for tungsten carbide burs. For diamond rotary instruments, zinc phosphate cement was significantly different from glass ionomer and Panavia-EX cements.

Analysis of Variance↗
PubMed2007

A comparison of terahertz pulsed imaging with transmission microradiography for depth measurement of enamel demineralisation in vitro.

Terahertz pulsed imaging (TPI) is a relatively new, non-ionising and non-destructive imaging technique for studying hard tissues which does not require tooth section preparation, unlike transmission microradiography (TMR). If TPI can measure the depths of caries/demineralisation lesions accurately the same tooth samples could be reused and remeasured during in vitro and in situ studies on de- and/or re-mineralisation. The aim of this study was to compare TPI and TMR for measuring the depths of a range of artificially induced bovine enamel demineralised lesions in vitro. Bovine slabs with artificial caries, induced to different levels of demineralisation by two different but standard demineralisation techniques ('acid gel' and 'carbopol') were measured by TPI and TMR and the readings compared. The set of TPI/TMR measurements obtained on the gel-demineralised slabs showed an extremely high coefficient of determination (r(2) = 0.995). Detailed analysis of the results and theoretical considerations (involving the relationship between refractive index profiling and mineral loss profile) are used to explain the findings and show that for acid gel lesions TPI is measuring demineralisation in the range of 47% of that of TMR depth plus an intercept of 16 microm, with further calculations allowing the TMR depths to be determined to within 5% using TPI.

Acids↗
PubMedDate not supplied

Find canals faster through basic research.

Achieving access and finding canals are the key first steps in the endodontic procedure. This has always been a time-consuming, qualitative procedure that relies on the dentist's experience and feel. Recent basic research has been published that shows that the anatomic morphological measurements concerning the pulp chamber are very consistent in every tooth. This research points the way to a quantitative, predictable and quick technique for making endodontic access preparations without risk. The research and clinical technique are described in this article.

Dental Pulp↗
PubMed1996

Bacterial penetration of the root canal of intact incisor teeth after a simulated traumatic injury.

One of the aims in treating traumatised teeth is to maintain the vitality of the pulp or allow conditions favourable for pulp revascularisation. However, infection of the pulp and root canal system may prevent this. A number of pathways have been proposed that allow bacteria to invade the root canal system, however most of these pathways cannot account for pulp infection in teeth that did not sustain injury to the periodontal attachment. Enamel/dentine cracks have been proposed as a portal for bacterial invasion of seemingly intact teeth and the aim of this study was to determine if bacteria could invade the root canal system after a simulated traumatic episode. Twenty intact and sound upper central incisors were chosen and prepared. One tooth was selected as a sterility control and the external crown surface of the remaining 19 teeth was subjected to infection with Streptococcus gordonii in a bacterial microleakage model. Over 7 days samples of growth media from the root canal system were taken and tested for bacteria. Sixteen of the teeth did not demonstrate bacterial invasion over the time frame. These teeth were then prepared for testing in a pendulum impact device and were subjected to a blow which did not fracture the crowns or dislodge the tooth from its simulated alveolus. The teeth were then prepared and tested in the bacterial microleakage model. After impact seven of the teeth demonstrated bacterial invasion of the root canal system (P = 0.002). These teeth were then reprepared for testing in the bacterial microleakage model. The crowns of five teeth, selected at random, were coated with two layers of light cured unfilled resin, the remaining two were used as positive controls. All the teeth coated with resin did not demonstrate bacterial invasion (P = 0.00), while the positive controls demonstrated invasion. The results suggested that enamel/dentine infractions were pathways for bacterial invasion of the root canal system of traumatised teeth. The application of unfilled resin to the anatomical crown prevented infection.

Dental Enamel↗
PubMed1997

Long-term success rate of resin-bonded metal crowns on the canine teeth of working dogs.

In this clinical study, 19 full metal crown restorations of canine teeth were placed in seven working dogs. Thirteen canine teeth were severely abraded with no involvement of the pulp cavities; six fractured canine teeth were endodontically treated. At least 1/3 of the coronal part of the canine tooth was available for a supragingivally performed, minimal tooth crown preparation. An adhesive technique to bond the electrolytically etched crown (an alloy of cobalt-chrome-molybdenum) to the tooth was used. The metal crowns, slightly shorter and with a rounder tip than the original tooth, were bounded to the enamel and dentine by using a resin luting cement. Posts or post-and-core techniques were not used. Mean follow-up period was 32 months (range 24-52 months), at which stage 17 crowns were found to be intact and functional. Two crowns were lost as a result of trauma resulting in a fracture of the tooth below the crown.

Acrylic Resins↗
PubMed2001

Periodontal regeneration of a class II furcation defect utilizing a bioabsorbable barrier in a human. A case study with histology.

This case report describes human histologic data of periodontal regeneration following guided tissue regeneration therapy (GTR) with a bioabsorbable barrier composed of polylactic acid. The tooth that was examined was part of a previously published study of the clinical effects of GTR therapy without the use of bone or bone substitutes on Class II furcation defects. Twenty-five months following the surgical procedure, the tooth was extracted for non-periodontal reasons. During this extraction, the bone within the furcation that was treated in the study was luxated with the tooth. At the completion of the study (month 12), the furcation's vertical probing depth had decreased by 2 mm with a 2 mm gain in clinical attachment. The horizontal furcation measurement decreased by 3 mm. Following extraction, the tooth was prepared for light microscopy and sectioned in the mesial-distal plane. Reference notches were not placed in the tooth at the time of surgery as there were no plans to perform histologic analysis in the study. However, using the buccal root prominences and what we interpreted to be root planing marks on the cementum, we were able to demonstrate that complete periodontal regeneration occurred on the root surface that was exposed to the pocket environment prior to surgery. New alveolar bone, cementum, and periodontal ligament were consistently observed throughout the furcation in the areas that demonstrated clinical attachment gain and a decrease in horizontal probing depth. This case report adds to the accumulating evidence of histologic periodontal regeneration following guided tissue regeneration with bioabsorbable polylactic acid barriers.

Absorbable Implants↗
PubMed1991

Amelogenin post-secretory processing during biomineralization in the postnatal mouse molar tooth.

The primary structures, molecular genetics and biosynthesis of the amelogenin protein of the developing tooth are established, but knowledge of their subsequent post-secretory processing and its relation to enamel biomineralization is fragmentary. Preparations of tooth matrix proteins were isolated from molars (M1) of mice from birth to 15 days and analysed by SDS-PAGE and immunochemical methods. Amelogenin proteins, isolated and partially purified by HPLC, were characterized by amino acid analysis and SDS-PAGE. At birth a 26 kDa amelogenin was present that during subsequent developmental stages generated a series of 20-25 kDa amelogenins differing in apparent size by approximately 1 kDa. Amino acid analyses showed that all these amelogenins have amino-terminal TRAP sequences; analyses for both glycosylation and phosphorylation were negative. It is suggested that these post-secretory amelogenins are generated by a sequence of specific carboxy-terminal cleavages, and that the observed post-secretory processing of amelogenin is functionally linked to the structure of the enamel matrix and the control of crystallite development.

Age Factors↗
PubMed1998

The effect of dentine surface treatment on pulpward pressure transmission during crown cementation: a laboratory study.

Thirty extracted human premolars received standardised full crown preparations. The teeth were randomly assigned into three groups: smeared (control), etched (phosphoric acid gel), and bonded (Scotchbond MP). Each tooth was perfused with saline to establish perfusion rates at baseline for all groups, and the post-etching stage for etched and bonded groups, post-bonding stage for bonded group, and post-cementation stage for all groups. Crowns made with four layers of die-spacing were cemented with zinc phosphate cement at 100N. Pulpal pressures were measured with a pressure transducer. It was concluded that dentine bonding agents may have the potential to reduce pulpal damage caused by pressure transmission from cementation.

Acid Etching, Dental↗
PubMed1990

The thresholds of the jaw-opening reflex and trigeminal brainstem neurons to tooth-pulp stimulation in acutely and chronically prepared cats.

Electrical stimuli were applied to tooth-pulp in cats and the thresholds of the jaw-opening reflex and of neurons in the trigeminal sensory nuclei were determined. The effects of the method of preparation of the animal for stereotaxic recording were determined by making observations on animals set up in one of three ways: acutely in the usual manner; chronically, three to five days before recording; and acutely with precautions to minimize nociceptive input to the central nervous system. The threshold of the jaw-opening reflex increased progressively during the setting up of the normal, acute preparations and at the time brainstem recording began was significantly higher in these than in either the chronic or low-trauma acute preparations. Previous studies have shown that the increase in threshold is maintained for several hours and is not due to the effects of the anaesthetic. In normal acute preparations, few units (27/154) were found that had thresholds below 50 microA, 0.1 ms, whereas many units were encountered that responded to such a stimulus in chronic (147/152) and low-trauma acute (99/127) animals. In the chronic and in low-trauma acute preparations, there was no significant difference between the thresholds of the units in the main sensory trigeminal nucleus and spinal subnucleus oralis compared with those in subnucleus caudalis. Thus the preparation of an animal for stereotaxic recording can cause a severe and long-lasting depression in the excitability of neurons in the trigeminal sensory nuclei and an increase in the threshold of the jaw-opening reflex. This effect will have influenced the results of previous studies on the responses evoked in central neurons by stimulation of tooth-pulp, and may have similarly affected recordings from other regions.

Anesthesia↗