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Biomedical subjects

H H Messer

Publications and source records attributed to H H Messer.

At least 37 records · Page 2Linked to original sources
PubMed2001

Effect of stress on acid dissolution of enamel.

OBJECTIVES: This study was designed to measure the dissolution of buccal enamel of extracted teeth exposed to acid with or without simultaneous cyclic occlusal loading. METHODS: Twenty mandibular premolars were mounted in pairs in a servohydraulic testing machine, and immersed in 1% lactic acid (pH 4.5) or water. One tooth of each pair was subjected to cyclic loading (100 N at 2 Hz for 200,000 cycles), with the load applied at 45 degrees to the tooth axis on the buccal incline of the buccal cusp. The second tooth of each pair was immersed in acid but not subjected to load. Control teeth were immersed in water, with one tooth of each pair undergoing cyclic loading. Impressions of the teeth were taken before and after exposure to acid and occlusal loading, and a profiling system was used to measure the depth and volume loss of enamel on the buccal surface. RESULTS: The depth of enamel dissolved ranged from approximately 50-200 microm. In certain locations teeth undergoing cyclic loading during acid exposure showed greater volumetric loss than teeth not subjected to load. Loaded teeth showed a complex pattern of enamel dissolution; volumetric loss in the cervical third was greater than in the middle third, and was much greater in the mesiobuccal segment (under tension) than in the distobuccal segment (under compression). Unloaded teeth showed greater volumetric loss in the cervical third than in the middle third, with a uniform pattern of enamel dissolution from mesiobuccal to distobuccal aspects. SIGNIFICANCE: Enamel dissolution is increased significantly in sites subjected to cyclic tensile load.

Analysis of Variance↗
PubMed2001

Comparison of methods for measuring cuspal deformation in teeth.

OBJECTIVES: The aim of this study was to compare two techniques of measuring cuspal deformation under occlusal load: Direct Current Differential Transformers (DCDTs) and strain gauges. The study investigated the relative dependence of the two techniques on the vertical orientation of the tooth in relation to direction of loading and differences in the patterns of change in response to a cavity preparation sequence. METHODS: Strain gauges and DCDTs were attached to the buccal and lingual surfaces of extracted maxillary premolars and mandibular molars. Premolars were subjected to simulated occlusal loads at varying vertical angulations before and after MOD cavity preparation. Molars were tested at progressive stages of cavity preparation. Cuspal deformation was recorded as linear cusp displacement (in microm, using DCDTs) and as cuspal strains (using strain gauges) and relative stiffness. RESULTS: Strain gauges were much less sensitive than linear displacement devices to vertical orientation of teeth, and computation of relative stiffness further reduced the effect of angulation. Strain gauges are much easier to use experimentally. DCDTs required precise three-dimensional adjustments for the testing of cuspal deformation. Patterns of change in cuspal flexure following cavity preparation were very different using the two techniques. CONCLUSIONS: Use of both devices simultaneously yielded much more information than when used alone, and showed that cusps do not deform as simple cantilever beams.

Analysis of Variance↗
PubMed2001

An investigation of cuspal deformation and delayed recovery after occlusal loading.

OBJECTIVE: The purpose of this study was to investigate the extent of progressive cuspal displacement during prolonged occlusal loading (either continuous or cyclic) and delayed cuspal recovery following removal of the load. METHODS: Extracted maxillary premolars with extensive MOD cavity plus endodontic access were subjected to an occlusal load applied to both cusps, followed by a recovery period. Two types of loading were applied: (a) continuous load of 100, 200 and 300 N for 0.1--1000 s; (b) cyclic loading of 300 N at 0.83 Hz for 1--1000 cycles. Cuspal displacement during loading and subsequent recovery were measured with an extensometer attached to both cusps. RESULTS: Continuous loading led to progressive cuspal displacement that was both time- and load-dependent. After removal of the load, complete recovery from cuspal deformation was prolonged up to 20 min, also in a time- and load-dependent manner. Cyclic loading resulted in a cumulative increase in cusp displacement but to only a very small extent (approximately 1 microm after 1000 cycles). CONCLUSIONS: Progressive cuspal displacement and delayed recovery occur with prolonged continuous or cyclic occlusal loading. Continuous loading (e.g. as in clenching) is potentially more damaging than cyclic loading (as in chewing).

Analysis of Variance↗
PubMed2001

Periodontal response to two intracanal medicaments in replanted monkey incisors.

Intracanal medicaments are recommended for use in replanted teeth to inhibit inflammatory root resorption. This study compared the effect of calcium hydroxide (Pulpdent) and a corticosteroid-antibiotic paste (Ledermix) on periodontal healing and root resorption following replantation. Incisors of eight Macaca fascicularis monkeys were extracted, stored dry for 15 min and replanted. After 11 days, root canals in two adjacent maxillary incisors were treated with one medicament and contralateral incisors with the other medicament, or left as untreated controls. Animals were sacrificed 8 weeks later and the teeth prepared for histomorphometric evaluation of periodontal ligament inflammation and root resorption. Periodontal ligament inflammation and inflammatory root resorption were markedly inhibited by both calcium hydroxide and corticosteroid-antibiotic relative to untreated controls. Replacement resorption was lowest in the corticosteroid-antibiotic group, and significantly (P<0.05) more normal periodontal ligament was present in this group (79.6%) than in calcium hydroxide and control groups (64.6% and 62.7%, respectively). Treatment with the corticosteroid-antibiotic inhibited inflammatory resorption and was slightly more effective than calcium hydroxide in producing a periodontal healing response.

Animals↗
PubMed2001

Effect of removal of the smear layer on apical microleakage.

It has been shown previously that the smear layer created during instrumentation of the root canal promotes apical microleakage. The purpose of the present study was to investigate the effect of removal of the smear layer on apical microleakage, using the fluid filtration method. Thirty-six single-rooted human premolar teeth were used. Six of the teeth were selected randomly as controls, and the remaining 30 teeth were randomly divided into two groups of 15 teeth each. For the first group (group 1) teeth were irrigated with NaOCl only (smear layer not removed). In the second group (group 2) the teeth were irrigated with 15% EDTA, followed by NaOCl to remove the smear layer. Both groups were filled with thermoplasticized gutta-percha (Obtura II) using glass-ionomer cement as sealer. All teeth were stored at 37 degrees C and 100% humidity for 2 days. Apical microleakage of the filled root canal was measured by the fluid filtration technique. Hydraulic conductance was measured by the movement of an air bubble in a capillary tube after a pressure of 200 mm Hg was applied to the system. The mean microleakage rate of group 1 and group 2 were 13.0 (SD +/- 5.1) and 16.9 (SD +/- 15.3) nl/s, respectively. Removal of the smear layer caused significantly more apical microleakage (p < 0.05, Student's t test) than when the smear layer was left intact.

Bicuspid↗
PubMed2001

The quality of clinical fit of stainless steel bands used in endodontics.

Stainless steel bands are commonly advocated to protect posterior teeth against fracture during endodontic treatment and before final restoration. A poorly fitting band, however, may lead to a compromised coronal seal and gingival irritation. This radiographic study assessed the quality of fit and marginal adaptation in the proximal area of stainless steel bands placed during routine endodontic treatment. Clinical radiographs of 120 maxillary and mandibular premolars and molars were evaluated. All radiographs were taken during routine clinical endodontic treatment and randomly selected from cases completed by ten operators. Approximately one-half of cases did not meet the criteria of adequate marginal seal (mesial: 65/120; distal: 49/120). Only 11 teeth were found to have adequate fit of the band on both mesial and distal aspects of the tooth. The most common reason for inadequacy of fit was lack of band adaptation to the tooth contour in the cervical region. Stainless steel bands have a high possibility of poor marginal fit and should be used with the awareness that they may produce other clinical problems.

Bicuspid↗
PubMed2001

Anisotropy of tensile strength of root dentin.

An effect of dentinal tubule orientation on mechanical properties of dentin has been difficult to demonstrate. We have tested the hypothesis that ultimate tensile strength (UTS) of dentin is affected by tubule (and hence collagen fibril) orientation. The UTS of human root dentin was investigated by direct tensile and diametral testing of specimens of known orientation prepared from extracted teeth. Dumbbell-shaped samples were machined for direct tensile testing (load parallel or perpendicular to tubule direction) and cylinders for diametral testing (load at 0 degrees, 45 degrees, 67.5 degrees, and 90 degrees). Fractured surfaces were examined by SEM. UTS was lowest when the tensile force was parallel to tubule orientation, and greatest at 90 degrees to tubule orientation (fracture parallel to tubule direction). SEM views of fractured surfaces suggested that microstructure contributes to fracture patterns. At least for properties involving disruption of the collagen matrix, root dentin shows a definite anisotropy.

Analysis of Variance↗
PubMed2000

Strain patterns in cervical enamel of teeth subjected to occlusal loading.

OBJECTIVES: This study was planned to investigate the variations in strains in enamel under different patterns of occlusal loading, using three-dimensional finite element analysis (3D FEA) and strain gage measurements in extracted teeth. METHODS: A 3D FEA model of a mandibular second premolar was used to investigate effects of occlusal load on enamel surface strains, particularly in response to oblique directions of cuspal loading. Point loads of 100 N were applied axially and at 45 degrees from the vertical on the buccal or lingual incline of the buccal cusp, either in the bucco-lingual plane or at varying mesio-distal angulations (up to +/- 20 degrees). Patterns of strain observed in the FEA model were confirmed experimentally using strain gages on extracted premolars mounted in a servohydraulic testing machine. RESULTS: Strains predicted from the FEA model were in excellent agreement with the strain gage measurements. Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction. A vertical load on the buccal cusp tip resulted in compressive strains on the buccal surface but small tensile strains in lingual cervical enamel. Strains resulting from oblique loads on buccal cusp inclines were complex and asymmetric, with either tension or compression occurring in any location depending on the site and angle of loading. SIGNIFICANCE: The magnitude, direction and character of strains in cervical enamel are highly dependent on patterns of loading. The asymmetric pattern of strains in buccal cervical enamel in response to oblique occlusal forces is consistent with the common clinical picture of asymmetric non-carious cervical lesions.

Analysis of Variance↗
PubMed2000

A new imaging technique for measuring the surface strains applied to dentine.

OBJECTIVES: To investigate possible variation in directional material properties of dentine in relationship to tubule orientation using a new optical imaging technique. METHOD: The optical imaging technique records photometrically a grid pattern formed by using a transmission electron microscope grid as a template on the polished surface of the dentine. The grid pattern is silhouetted onto the sample surface using standard techniques. Compression (c) and diametral compression (dc) tests were undertaken using a servo hydraulic testing machine (MTS model 810) acting on rectangular blocks of dentine with dimensions 1.5 x 1.0 x 1.0 mm (for c) and cylindrical samples with dimensions 2.1 mm in diameter and 1-1.5 mm thick (for dc), respectively. The samples were cut using a diamond wheel and miniature lathe and the cut surfaces polished. Images due to a changing load profile were captured and stored as digitised files on a computer for later analysis. The precision is mainly determined by the pixel resolution of the charged-coupled device camera. RESULTS: Preliminary results show the value of elastic modulus of dentine (10.4 +/- 2.9 GPa) to be similar to those previously reported in the literature. Very small localised strains at the surface of a sample can be observed qualitatively and measured quantitatively by reference to the line spacing (approximately 85 microns). Maximum strength varied with tubule orientation and (compressive/tensile) stress. CONCLUSION: Very small samples of dentine may be investigated for strain in more than one direction using the imaging technique described. These results may be more appropriate for finding relative directional change rather than obtaining the elastic properties of the dentine.

Compressive Strength↗
PubMed2000

Torque during canal instrumentation using rotary nickel-titanium files.

Nickel-titanium engine-driven rotary instruments are used increasingly in endodontic practice. One frequently mentioned problem is fracture of an instrument in the root canal. Very few studies have been conducted on torsional characteristics of these instruments, and none has been done under dynamic conditions. The purposes of this study were to measure the torque generated and the apical force applied during instrumentation with a commercial engine-driven nickel-titanium file system, and to relate torque generated during simulated clinical use to torsional failure of the instruments. Ten extracted human teeth (five with small-sized and five with medium-sized straight root canals) were instrumented with Quantec Series 2000 files, and the torque and apical force generated were measured. The applied apical force was generally low, not exceeding 150 g in either small or medium canals. The torque depended on the tip size and taper of each instrument, and on canal size. Instruments with 0.05 and 0.06 taper generated the highest torque, which was greater in small than in medium canals. The torque at failure was significantly (p < 0.001) higher than torque during instrumentation, but with considerable variation in the extent of the difference.

Analysis of Variance↗
PubMed2000

Defects in rotary nickel-titanium files after clinical use.

The purpose of this study was to analyze the type and frequency of defects in nickel-titanium rotary endodontic files after routine clinical use, and to draw conclusions regarding the reasons for failure. All of the files (total: 378, Quantec Series 2000) discarded after normal use from a specialist endodontic practice over 6 months were analyzed. Almost 50% of the files showed some visible defect; 21% were fractured and 28% showed other defects without fracture. Fractured files could be divided into two groups according to the characteristics of the defects observed. Torsional fracture occurred in 55.7% of all fractured files, whereas flexural fatigue occurred in 44.3%. The results indicated that torsional failure, which may be caused by using too much apical force during instrumentation, occurred more frequently than flexural fatigue, which may result from use in curved canals.

Dental Alloys↗
PubMed2000

Review of One-Visit Endodontic Treatment.

Like the proverbial curate's egg, this CD-ROM is good in parts. I plan to use some sections in preclinical teaching, because the three-dimensional animations clarify descriptions for students unfamiliar with endodontic concepts. The rationale for single-visit endodontics is too inclusive for Australian audiences, and not adequately based on scientific evidence.

CD-ROM↗
PubMed1999

Load and strain during lateral condensation and vertical root fracture.

Vertical loads and root surface strains in extracted teeth during lateral condensation using finger and hand spreaders were measured and compared with loads and strains at fracture. Six groups each of 10 teeth were tested: maxillary central incisor, premolar and molar; and mandibular incisor, premolar and molar. Root strains were measured using strain gauges mounted on the apical and middle third of the buccal root surface. Statistical analysis was performed at the 95% level of confidence. The maximum loads and strains generated by finger spreaders were significantly lower than those generated using a hand spreader (D11T). These loads and strains were also significantly lower than the values at fracture. Most fracture lines were in a buccolingual direction, but maxillary premolars with two separate roots and the mesiobuccal root of maxillary molars showed more variation in fracture site. The results suggest that lateral condensation alone should not be a direct cause of vertical root fracture. The use of finger spreaders, however, is associated with lower risk.

Analysis of Variance↗
PubMed1999

Effect of matrix placement on furcation perforation repair.

Furcation perforations are a serious complication during endodontic treatment, and a matrix to aid placement of repair material has been recommended. This study tested the sealing ability of amalgam and Ketac silver placed with and without plaster of Paris as a matrix. A bacterial penetration technique was used to test the seal. Perforations created in the pulpal floor of extracted human mandibular molars were repaired as follows: group 1, amalgam; group 2, amalgam plus plaster as a matrix; group 3, Ketac silver; and group 4, Ketac silver plus plaster (17 teeth/group). Leakage was measured by placing bacteria (Streptococcus sobrinus) in the pulp chamber, and recording the time taken for bacterial growth in a medium bathing the root surface. A plaster of Paris matrix improved the seal with amalgam, but not with Ketac silver. Ketac silver provided the best seal, but all materials showed complete leakage within 22 days.

Calcium Sulfate↗
PubMed1999

Clinical judgement and decision making in endodontics.

Clinical judgement in endodontics consists of much more than diagnosis and treatment planning for the affected tooth. The issues involved in clinical judgement and decision making can be summarised by three questions: 1. Is endodontic treatment appropriate for the patient? Endodontic treatment should be undertaken only as part of an agreed, comprehensive treatment plan that takes into account patient concerns as well as objective clinical findings. 2. How difficult is the endodontic treatment? The difficulty of the case should be balanced with the skill and experience of the dentist, in deciding whether to manage the case in general practice or to refer the patient to an endodontist. The use of a standard form for assessing the difficulty of each endodontic case will aid in consistent, systematic assessment of patients. An example of such a form is provided. 3. What is the prognosis for the tooth? The outcome of endodontic treatment depends not only on the endodontic treatment but on other factors such as restorability and periodontal status. The prognosis will be compromised by procedural problems and by restorative and periodontal factors. In all but routine cases, the steps involved in decision making may be more complex and less easily resolved than the practical clinical aspects of endodontic therapy.

Clinical Competence↗
PubMed1998

Detectability of artificial periapical lesions using direct digital and conventional radiography.

The ability of different radiographic techniques to detect the presence of artificially created periapical lesions in mandibles of human cadavers was investigated. Conventional radiography was compared with direct digital imaging using the Digora system. Artificial lesions were created around the roots of molars in three stages: removal of lamina dura only, extension to cancellous bone, and involvement of cortical plate. Radiographs and digital images (gray scale, color, and reverse image) were obtained preoperatively and after each stage of bone removal. Images were scored on a 5-point scale by eight observers. For all image types, lesions were readily detectable after removal of lamina dura only, with increasing detectability associated with further bone removal (especially cortical plate involvement). Radiographs and gray-scale digital images were comparable at all stages, whereas color and reverse images were associated with a greater spread of diagnostic scores. Digital imaging did not enhance detectability of lesions.

Alveolar Bone Loss↗
PubMed1998

Effects of interleukin-1 beta on human pulpal fibroblast proliferation and collagen synthesis.

The aim of this study was to investigate the effect of interleukin-1 beta (IL-1 beta) on pulpal fibroblast proliferation and collagen synthesis in vitro. Cell proliferation was assessed by [3H]thymidine uptake at 24, 48, and 72 h. These cells were compared with dermal fibroblasts under a range of conditions. IL-1 beta inhibited pulp cell proliferation, but this effect was decreased by the presence of indomethacin. In contrast, IL-1 beta stimulated dermal fibroblast proliferation in the absence and presence of indomethacin. Collagen synthesis was analyzed by incorporation of 5-[3H]proline into polypeptide chains. IL-1 beta stimulated synthesis of type I collagen both in the absence and presence of indomethacin. Results suggest that the inhibitory effect on pulp cell proliferation is dependent upon IL-1 beta-induced prostaglandin E2 synthesis and that IL-1 beta is a potent mediator of prostaglandin E2 synthesis in dental pulp. These observations imply a role of IL-1 beta in collagen synthesis, but not in the fibroblast proliferation phase of the healing process.

Analysis of Variance↗