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At least 397 records · Page 22Linked to original sources
PubMed2004

Analysis of strain around endosseous dental implants opposing natural teeth or implants.

STATEMENT OF PROBLEM: Natural teeth and implants have different force transmission characteristics to bone. PURPOSE: The purpose of this study was to compare strains induced around a natural tooth opposing an implant with strains around occluding implants under static and dynamic loads. MATERIAL AND METHODS: Occlusion was created between a natural molar tooth and an implant in 1 side, and 2 implants in the contralateral side of acrylic resin models of both jaws. Strain-gauges were bonded around the neck of the natural tooth and implants, and strains were measured under 75 N and 100 N static axial and lateral dynamic loads in separate load situations using a data acquisition system at sample rate of 1000 Hz. The strain data of the natural tooth and implants were compared for each load by Kruskal-Wallis testing followed by the multiple comparison test (alpha=.05). RESULTS: Compressive strains were induced around natural tooth and implants as a result of static axial loading, whereas combinations of compressive and tensile strains were observed during lateral dynamic loading. Strains around the natural tooth were significantly lower than the opposing implant and occluding implants in the contralateral side for most regions under all loading conditions ( P <.05). There was a general tendency for increased strains around the implant opposing natural tooth under higher loads and particularly under lateral dynamic loading ( P <.05). CONCLUSION: Under static and dynamic loads, strain magnitudes around a natural tooth were significantly lower than that of an opposing implant and occluding implants in the contralateral side.

Bite Force↗
PubMed2005

Finite element analysis of mechanism of cervical lesion formation in simulated molars during mastication and parafunction.

STATEMENT OF PROBLEM: The mechanical theory of cervical lesion formation is popular; however, the mechanism of formation of these lesions is not fully explained. PURPOSE: The aim of this study was calculation of the stresses and Tsai-Wu strength ratio in the cervical area of the mandibular molar during grinding, clenching, and mastication, as well as theoretical investigation of the mechanism of cervical lesion formation in teeth. MATERIAL AND METHODS: A 2-dimensional finite element model of the mandibular first molar and crown of the opposing maxillary molar in the frontal section was developed. Computational simulation of mastication of a bolus with high elastic modulus, including grinding and clenching, was performed. Pairs of contact elements were used between the bolus and occlusal surfaces of the teeth. The analysis was nonlinear. During these simulations, the pressure exerted on the occlusal surface and the state of stresses in the mandibular molar were calculated. To evaluate the strength of anisotropic tooth tissues, the Tsai-Wu failure criterion was applied. This criterion considers the difference in strength of materials due to tensile, compressive, and shear stresses. RESULTS: Significant pressures were exerted on lingual cusps of the mandibular molar model during computer simulations of physiological and pathological load. In enamel elements close to the buccal cemento-enamel junction (CEJ) of the studied tooth, tensile stresses were observed which exceeded the strength of the enamel. In this area, the Tsai-Wu strength ratio reached values higher than 1. According to the Tsai-Wu criterion, these elements were damaged and, thus, were removed from the computer tooth model. During subsequent modeling of the tooth with the initiated cervical lesion, the Tsai-Wu ratio exceeded 1 along the dentino-enamel junction (DEJ), creating an overhang of enamel in the cervical area. Application of minimal horizontal force caused a fracture of this fragile, unsupported enamel fragment. CONCLUSIONS: Overloading of theoretical teeth by computer simulation resulted in enamel damage at the CEJ and led to initiation of a cervical lesion. Subsequent overloading resulted in enamel destruction along the DEJ. The overhanging enamel fragment may easily be chipped. This process was repeated during subsequent tooth overloading and caused enlarging of the lesion.

Anisotropy↗
PubMed2005

A comparison of 18 different x-ray detectors currently used in dentistry.

PURPOSE: There has been a proliferation of available dental x-ray detectors over the recent past. The purpose of this short technical report is to provide a basic comparison of spatial resolution, contrast perceptibility, and relative exposure latitudes of 18 current dental x-ray detectors, including solid-state systems (CCD and CMOS), photostimulable phosphors, and analog film. METHODS: Spatial resolution was measured using a 0.025 mm Pb phantom test grid with a measurement range from 1.5 to 20 lp/mm. For contrast perceptibility, a 7-mm thick aluminum perceptibility test device with wells of 0.1-0.9 mm depth at 0.1 mm intervals and 1 defect of 1.5 mm was used. The relative exposure latitude was determined by expert consensus using clear discrimination of the enamel-dentin junction as the lower limit and pixel blooming or unacceptable levels of cervical burnout as the upper limit. RESULTS: The highest spatial resolution was found with Kodak InSight film, RVG-ui (CCD), and RVG 6000 (CMOS) detectors, each of which achieved 20 lp/mm, followed by the Planmeca Dixi2 v3 at > or =16 lp/mm. Contrast resolution was at least to 0.2 mm through 7 mm aluminum for all 18 detectors, with the best results being found for the Visualix HDI, RVG-ui, RVG 5000, and RVG 6000 detectors and the Schick CDR wired and wireless systems. The greatest exposure ranges were found with photostimulable phosphors and the Kodak RVG 6000 and RVG 5000 detectors. CONCLUSIONS: Most current x-ray detectors generally perform well in terms of spatial and contrast resolutions, and in terms of exposure latitude. These findings were independent of the modality applied.

Contrast Media↗
PubMed2005

A case of multiple idiopathic external root resorption: a 6-year follow-up study.

Multiple idiopathic external root resorption of permanent teeth is a very infrequent phenomenon. This paper describes a case of multiple idiopathic external root resorption at cement-enamel junction in 21 of 25 teeth followed up for 6 years. In addition to clinical features and radiographs, we present results of histological and bacteriological examinations.

Bone Density Conservation Agents↗
PubMed2005

External cervical root resorption involving multiple maxillary teeth in a patient with hereditary hemorrhagic telangiectasia.

Hereditary hemorrhagic telangiectasia (HHT) is an inherited syndrome characterized by mucocutaneous telangiectases that commonly involve the tongue, lips, fingers, and conjunctiva. While root resorption has been reported in association with central hemangiomas of bone, the association of HHT with external cervical root resorption has not been described to date. We report a case of a 57-year-old female with HTT who presented with advanced cervical root resorption involving multiple maxillary anterior teeth. Histologic examination of the gingival tissue adjacent to the area of root resorption demonstrated multiple thin-walled vascular elements as well as larger vascular channels surrounded by a thickened muscular layer. We hypothesize that the external root resorption seen in this case is the result of the HHT-related vascular process in the adjacent gingival tissue.

Female↗
PubMed2007

Invasive cervical resorption: clinical and radiological diagnosis and treatment of 3 cases.

Invasive cervical resorption is a relatively uncommon form of external root resorption. Etiologic factors include trauma, orthodontic treatment, intracoronal bleaching, and inflammation, but invasive cervical resorption is often idiopathic. There may be no external signs of this disorder, and the resorptive lesion is often detected by routine radiographic examination. This article describes the clinical and radiological diagnoses and treatment modalities of invasive cervical resorption in 3 patients. Two of the 3 cases were incidental radiographic findings and the teeth concerned were symptom free. One case was symptomatic due to periodontal infection. Computed tomography (CT) evaluation was performed in the 2 symptom-free patients. Thus, exact size and localization of the resorptive lesions were obtained. In 2 cases, root canal treatment was performed, and in the other case the resorptive defect was sealed with mineral trioxide aggregate.

Adult↗
PubMed2004

Directing ultrasound at the cemento-enamel junction (CEJ) of human teeth: I. Asymmetry of ultrasonic path lengths.

The diagnosis of degenerative changes in human teeth is of general interest because early detections can avoid greater health problems and further weakening effects. Since the wear of teeth determines their stability and lifetime in relation to the physiological load, an ultrasonic survey of any dimensional changes of the enamel layer and especially of the dentin wall thickness may be very helpful. However, an ultrasonographic diagnosis requires first to determine the anisotropic human tooth properties at clinically relevant locations and to simulate wave propagation phenomena in inhomogeneous tooth models with proper dimensions. The first article of a series that provides modular data of mineralized tissues in human teeth at the cemento-enamel junction (CEJ) deals with an ultrasonic method for measuring the asymmetry of dimensional characteristics of extracted human teeth and their ultrasonic path lengths (UPL). Heavily attenuating tooth halves were investigated with respect to the symmetry of normal and inclined oppositely directed radial ultrasonic paths. The measured UPLs ranged from 1.2 mm to 4.4 mm. The relative difference in inclined UPLs between the left and the right tooth halves reaches almost 30%. This reveals a large asymmetry. The mean difference of angles that represent fastest path lengths was 2.2+/-8.1 degrees, which indicates large asymmetry and anisotropy. Several aspects, which are required for a proper integration of asymmetric data into models designed for medical element engineering and simulation (MEES), are discussed.

Algorithms↗
PubMed2001

A review of interproximal wear grooves on fossil hominin teeth with new evidence from Olduvai Gorge.

Interproximal (approximal) grooves at the cementum-enamel junction of premolar and molar teeth have been observed in a broad range of human ancestors and related extinct species from 1.84 million years ago to the present. Many hypotheses have been presented to explain the aetiology of these grooves, though their form and positioning are most consistent with tooth-picking behaviours. This paper reviews occurrences of interproximal grooves in the cheek teeth of modern and fossil humans, evaluates hypotheses on their cause, and reports on a previously undescribed groove found in OH 60, a molar tooth from Olduvai Gorge. This specimen is among the earliest to show such grooving, and is most likely attributable to Homo erectus. It is concluded that, because interproximal grooves have been observed only on Homo teeth, they probably reflect a behaviour or behaviours unique to that genus.

Animals↗
PubMed1998

Toothbrushing abrasion of polyacid-modified composites in neutral and acidic buffer solutions.

STATEMENT OF PROBLEM: Polyacid-modified composites are recommended for use in lesions that are subjected to toothbrushing abrasion and acidic challenges, such as cervical lesions. There is little information whether these materials are able to withstand degradation due to erosive attacks and toothbrushing abrasion. PURPOSE: This study evaluated the resistance of polyacid-modified composites against toothbrushing abrasion under acidic and neutral conditions. METHODS: Forty specimens fabricated of each of two polyacid-modified composites (Dyract, Compoglass) were investigated. For each composite group, 20 specimens were placed in a neutral solution (pH: 6.8) and 20 specimens were placed in an acidic solution (pH: 3.0) for 24 hours. All specimens were brushed in an automatic toothbrushing machine, then subjected to storage in the respective buffer solution (8 hours), followed by brushing three times. Abrasion was determined profilometrically. RESULTS: For both materials, abrasion in the acidic environment was significantly higher compared with neutral conditions. Thus, Compoglass composite demonstrated a lower abrasion resistance than Dyract composite. CONCLUSION: The abrasion resistance of the investigated materials was reduced under acidic conditions.

Acids↗
PubMed1998

Sealing ability of two "compomers" applied with and without phosphoric acid treatment for Class V restorations in vivo.

STATEMENT OF PROBLEM: "Compomers" are being used with increasing frequency in Europe and North America. PURPOSE: This study evaluated the marginal seal of two compomers in vivo. MATERIAL AND METHODS: Periodontally involved teeth, scheduled for extraction, were selected. Four groups of a combination of materials were used (Dyract with Dyract-PSA primer, group 1; Dyract with Prime and Bond 2.0, group 2; Compoglass with SCA primer, group 3; and Compoglass with Syntac Single Component, group 4). The restorations were made in a standardized shaped cavity, across the cementoenamel junction, and the teeth were extracted after 2 to 3 months of clinical service. The specimens were kept in a solution of 2% methylene blue for 24 hours. After being embedded in epoxy resin, sections were made with a low speed saw along the longitudinal axis of the teeth. The examination of dye penetration was made with a microscope at a magnification of x20 and scoring was done at both coronal and apical sites. Kruskal-Wallis statistical analysis was performed at 5% significance level. RESULTS: Groups 2 and 4 scored significantly less than groups 1 and 3 and for groups 2 and 4, 30% of the restorations exhibited leakage. CONCLUSION: These restoration systems did not completely prevent leakage either at the incisal or the cervical margins. Therefore the use of an enamel-dentin bonding system in combination with the proprietary compomer is recommended.

Acid Etching, Dental↗
PubMed1999

Finite element stress analysis on the effect of splinting in fixed partial dentures.

STATEMENT OF PROBLEM: Long-span fixed partial dentures usually require splinting of multiple abutments to overcome mechanical problems associated with the long edentulous span. Most information and indications for the use of multiple splinted abutments have been empirically derived. PURPOSE: This study analyzed the stress levels in the teeth and supporting structures of a fixed prosthesis and ascertained how the addition of multiple abutments in a fixed prosthesis modifies the stresses and their deflection. MATERIAL AND METHODS: The finite element method was used to analyze mechanical behaviors of a prosthesis and its supporting structures when a fixed prosthesis with several designs replaced a mandibular second premolar and a first molar. Variations of the standard finite element model were made by changing the number of splinted teeth and the level of bone support. RESULTS: A reduction of stress and deflection was observed in the supporting structures when a fixed partial denture was fabricated and teeth were splinted together. Increasing the number of splinted abutments did not reveal a proportional reduction of stress in the periodontium. Stress concentrations were seen in the connectors of prosthesis and in the cervical dentin area near the edentulous ridge. CONCLUSION: Increasing the number of the splinted abutment did not compensate for the mechanical problems of a long-span fixed partial denture sufficiently.

Alveolar Bone Loss↗
PubMed1999

Microleakage of Class V resin-modified glass ionomer and compomer restorations.

STATEMENT OF PROBLEM: Resin-modified glass ionomers and polyacid-modified resin composites (compomers) have been introduced to provide esthetic restorations. However, there is concern about the marginal sealing ability of these materials, especially at the dentin (cementum) aspects of restorations. PURPOSE: This in vitro study evaluated the microleakage of Class V restorations made with resin-modified glass ionomers or a compomer. MATERIAL AND METHODS: Thirty noncarious human molar teeth were used. Standardized kidney-shaped Class V cavity preparations were placed in the buccal and lingual surfaces at the cementoenamel junction. Teeth were randomly assigned to 3 experimental groups of 10 teeth each and restored as follows: group 1, Fuji II LC; group 2, Vitremer; and group 3, Dyract. In all cases, the manufacturers' instructions were strictly followed. All materials were placed in a single increment. Unfinished restorations were immediately coated with the respective manufacturers' sealer or varnish and this was either light cured for 20 seconds or allowed to air-dry. After 24 hours, teeth were finished to contour and to the cavosurface margins, coated with nail varnish except for 1 mm around the restoration margin, thermocycled (1000x, 5-55 degrees C) and placed in a solution of 2% basic fuchsin dye for 24 hours at room temperature. The staining along the tooth restoration interface was recorded. RESULTS: Kruskal-Wallis 1-way analysis of variance revealed significant differences among all restorative materials for the overall, occlusal, and gingival scores (P =.03, P =.01, P =.01, respectively). Occlusal and gingival scores for each matched pair of restorative materials using the Wilcoxon test showed statistically significant differences between Fuji II LC glass ionomer cement and Dyract composite, both for the occlusal (P =.005) and gingival (P =.005) margins and also as an overall evaluation (P =.01), with Fuji II LC showing the least dye penetration. Vitremer revealed dye penetration scores not significantly different from Fuji II LC glass ionomer cement or Dyract composite. CONCLUSION: Resin-modified glass ionomers showed less or similar microleakage than the polyacid-modified composite resin tested.

Analysis of Variance↗
PubMed1996

Wound healing after mucoperiosteal surgery in the cat.

The purpose of this study was to examine possible tissue-dependent differences in rate of healing after mucogingival flap surgery. After intrasulcular incision and a vertical-releasing incision distal to the maxillary and mandibular cuspids, buccal, full-thickness mucogingival flaps were raised in four quadrants of 10 adult cats. The triangular flaps were left open for 30 min and then repositioned and sutured. Tissue reactions were studied histologically after 1, 3, 7, 14, and 28 days of healing. Although new collagen occasionally was observed in the wound space in the free gingiva at 3 days, collagenous union between the cut dentogingival fibers and the flap seemed well established at 7 days. Flap reattachment to the denuded cortical bone was seen at 14 days in the region of the attached gingiva. In the region of the alveolar mucosa, however, residual coagulum and inflammatory reaction was present as late as at 28 days in several specimens. These observations indicate a marked difference in rate of healing among the different interfaces involved. These variations seem to be related to variations in size of the resulting wound space when a full-thickness mucoperiosteal flap is readapted over cervical root surfaces, alveolar bone crest, and denuded cortical bone, respectively.

Animals↗
PubMed1996

Microleakage of human saliva through dentinal tubules exposed at the cervical level in teeth treated endodontically.

This study investigated the possibility of saliva recontamination occurring between the root canal wall and sealer through dentinal tubules exposed after the cementum was removed at the cervical level by root planing and treatment with citric acid. Thirty-four extracted human maxillary anterior teeth were randomly placed into five groups after chemomechanical preparation and obturation with gutta-percha and sealer; the sealer was allowed to set for 48 h. A ring 3 mm high, at the cervical level, was subjected to root planing, with complete removal of the cementum. All specimens were coated with two layers of nail polish and two layers of sticky wax, except for the ring subjected to root planing that was treated with citric acid for 30 s. The specimens were exposed to human whole saliva for 20 to 80 days and then immersed in dye to determine microleakage. Specimens were cleared and measurements made to the maximum point of dye penetration. All of the specimens exposed to saliva showed leakage except for the negative control, wherein no dye penetration was seen. Where leakage was found, the dye penetrated between the canal walls and the sealer to increasing depths, proportional to the time of exposure to the saliva. Statistical analysis confirmed these data, evidencing a difference between the means, which was highly significant for all pairs.

Analysis of Variance↗
PubMed1997

SEM examination of secondary dentine under and opposite cervical carious lesions.

The deposition of calcified secondary dentine underlying carious lesions and on the wall opposite to the carious lesions was examined in this study. Twenty single rooted human teeth were used in this work. The teeth were cleaned and fractured into two longitudinal halves, which were examined under a scanning microscope. The results showed complete disappearance of the dentinal tubules, globular mineralized deposits, and mineralized deposits of fibrous morphology underlying carious lesions, while on the dentinal walls opposite to the carious lesions were calsospherites, mineralized secondary dentine, and typical deposition of secondary dentine.

Adult↗
PubMed1998

The effect of the bleaching agent sodium perborate on macrophage adhesion in vitro: implications in external cervical root resorption.

The purpose of this study was to investigate the in vitro effect of sodium perborate, which is used as a bleaching agent in the treatment of discolored pulpless teeth, on substrate adherence capacity of macrophages. Inflammatory macrophages were obtained from Wistar rats and resuspended in RPMI-1640 medium. As a test of macrophage adhesion, the adherence capacity of macrophages to a plastic surface was determined. Assays were conducted in Eppendorf tubes for 15 min of incubation at 37 degrees C in a humidified atmosphere of 5% CO2. The adherence index was calculated. Results showed that sodium perborate decreased in a dose-dependent manner and decreased significantly (p < 0.05) the adherence index of rat peritoneal macrophages. Sodium perborate was less potent than sodium hypochlorite and eugenol in inhibiting macrophage adhesion. The inhibitory effect of sodium perborate on macrophage adhesion further supports the concept that this agent is not implicated in external cervical root resorption associated with intracoronal bleaching.

Animals↗
PubMed1998

Effects of CO2 laser in treatment of cervical dentinal hypersensitivity.

The effectiveness of CO2 laser therapy in the reduction and elimination of dentinal hypersensitivity in vivo and its thermal effects on tooth surfaces in vitro were investigated. Twenty-three patients with 91 sensitive teeth participated in this study and were followed for 3 months. The parameters used with CO2 laser were 1 W in a continuous wave mode and irradiation time ranging from 5 to 10 s. Hypersensitivity was assessed by thermal stimulus (a blast of air from a dental syringe). Thermal effects were measured by thermography using 10 extracted human teeth. After laser treatment, all patients were immediately free from sensitive pain. Over 3 months, the CO2 laser treatment reduced dentinal hypersensitivity to air stimulus by 50%. All teeth remained vital with no adverse effects. Thermography revealed no temperature increase on irradiated tooth surfaces subjected to water coolant. These results show that the CO2 laser is useful in the treatment of cervical dentinal hypersensitivity without thermal damage to pulp.

Adult↗