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At least 37 records · Page 2Linked to original sources

PubMed2004

Influence of placement techniques on Vickers and Knoop hardness of class II composite resin restorations.

OBJECTIVES: To analyze the influence of two placement techniques on Knoop and Vickers hardness of class II cavities restored using packable (A.L.E.R.T., Solitaire 2, SureFil) and conventional microfilled and hybrid (Filtek A110 and Z250, respectively) resin composites. METHODS: Fifty standardized class II cavities (5 x 3 x 1.5 mm3) were prepared in human premolars. They were divided into ten groups (n = 5) and restored according to each resin composite material (A.L.E.R.T., Solitaire 2, SureFil, Filtek A110 and Z250) and placement technique (incremental or bulk). After storage in distilled water at 37 degrees C for 24 h, they were thermal cycled (700 cycles/5-55 degrees C, 1 min dwell time) and sectioned longitudinally. One section from each specimen was embedded and polished for Knoop and Vickers hardness measurements. Sixteen indentations were performed for each restoration, eight on the occlusal and eight on the cervical surfaces. RESULTS: Results were submitted to ANOVA and demonstrated that all materials presented lower hardness values at the cervical surfaces when the bulk placement technique was employed, when compared to the occlusal surfaces (p< 0.001) whereas the same did not occur with the incremental technique. Pearson's correlation test demonstrated a positive correlation between Vickers and Knoop hardness numbers. SIGNIFICANCE: The use of bulk placement technique resulted in lower values of hardness at the cervical surfaces of class II restorations. Values obtained using Knoop hardness test showed a high correlation with Vickers hardness measurements.

Analysis of Variance↗

PubMed2004

Relation in color of three regions of vital human incisors.

OBJECTIVES: For an adequate color reproduction, it is very valuable to quantify the color distribution in human teeth accurately. The aim of this study was to determine the color relation between three tooth segments (cervical, middle and incisal) in vital upper central incisors, using digital photography. METHODS: Digital recordings of 64 upper right central incisors were made using a standardized head-camera setup. The L*a*b* values of three regions were attained from the standardized digital images using software. RESULTS: There were statistically significant linear correlations for L* and b* between the three tooth segments (all r's > or = 0.60; p < 0.001). The correlation coefficient for a* was lower compared to L* and b* values. The L* and b* values of cervical and incisal tooth segment could be calculated from L* and b* values of middle tooth segment. SIGNIFICANCE: These results show the potency for color mapping of a whole tooth surface by extrapolation of color values of only one part of the surface.

Adult↗

PubMed2006

Cuspal movement and microleakage in premolar teeth restored with resin-based filling materials cured using a 'soft-start' polymerisation protocol.

OBJECTIVES: To investigate the effect of polymerisation shrinkage strain of four posterior filling materials on cuspal movement, degree of conversion (DC) and cervical gingival microleakage of mesio-occlusal-distal (MOD) restorations placed incrementally in maxillary premolar teeth using a 'soft-start' polymerisation protocol. METHODS: Forty sound extracted upper premolar teeth were subjected to standardised preparation of a large MOD cavity before restoration. A 'soft-start' polymerisation curing regimen was used and each posterior filling material was placed in eight increments with the appropriate bonding system. A twin channel deflection measuring gauge allowed a measurement of individual cusp deflections at each stage of polymerisation. Restored teeth were thermocycled before immersion in a 0.2% basic fuchsin dye for 24h. After sagittal sectioning of the restored teeth in a mesio-distal plane, the sectioned restorations were examined to assess cervical microleakage. The DC was also assessed using a diffuse-reflectance accessory on a Fourier transform infra-red spectrophotometer. RESULTS: A significant increase in cuspal movement recorded for Z100 (20.06+/-4.71) compared with Filtek Z250 (16.52+/-3.26), P60 (14.23+/-3.71) and Admira (11.11+/-2.47). No significant reduction in cuspal movement was identified when compared with a previous study [6] where a full-intensity standard polymerisation protocol was employed. No significant differences were also identified between the materials when the cervical gingival microleakage scores or DC were examined for the 'soft-start' compared with the standard polymerisation protocol. CONCLUSIONS: Although material type remained a significant factor, the use of a 'soft-start' polymerization compared with a standard curing regime did not offer any significant reduction in associated cuspal movement, DC or gingival microleakage at the cervical dentine cavosurface margin of the cavities restored with the resin-based filling materials.

Bicuspid↗

PubMed2006

Three-dimensional finite element analysis of strain and stress distributions in endodontically treated maxillary central incisors restored with different post, core and crown materials.

OBJECTIVES: The present comparative analysis aimed at evaluating which combination of restorative materials resulted in the most homogeneous stress and strain distributions. METHODS: A three-dimensional finite element analysis was performed. All the nodes on the external surface of the root were constrained in all directions. Eighteen experimental models with different material properties and configurations were simulated. An arbitrary load of 10N was applied at 60 degrees angle with tooth longitudinal axis on the palatal surface of the crown. Von Mises (equivalent stresses) energetic criterion was chosen. RESULTS: In all the models the values of both strain and stress recorded at the middle third of the buccal aspect of the root surface were at their maxima. On the contrary, the minimum values were noticed at level of both the apical portion of the post and the root apex. The maximum stresses were evidenced at level of the cemento-enamel junction (CEJ) on both the buccal and palatal aspects of root cement and dentin. Stress progressively decreased from the outer to the inner part of the root and from the CEJ towards the incisal margin of the crown as well. SIGNIFICANCE: The results of the present study would allow clinicians to make an informed choice from among available materials to restore endodontically treated teeth.

Cementation↗

PubMed2006

Clinical long-term retention of etch-and-rinse and self-etch adhesive systems in non-carious cervical lesions. A 13 years evaluation.

OBJECTIVES: The aim of this study was to evaluate the clinical long-term retention to dentin of seven adhesive systems. METHODS: A total of 337 Class V restorations of three three-step etch-and-rinse, one two-step etch-and-rinse and three self-etch adhesive systems were placed in non-carious cervical lesions without intentional enamel involvement. The restorations were evaluated at baseline and then every 6 months during a 13 years follow-up. Dentin bonding efficiency was determined by the percentage of lost restorations. RESULTS: During the 13 years, 275 restorations could be evaluated. The cumulative loss rate at 13 years was 60.3%, with significant different failures rates for the different systems varying between 26.3 and 94.7%. Three materials fulfilled the ADA 18 months full acceptance criteria. Three systems showed already at 18 months or earlier catastrophical debonding rates. The annual failure rates for the three-step etch-and-rinse systems were: Allbond 2 4.1%, Clearfil LB 2.0% and Denthesive 7.3%. For the two-step etch-and-rinse Gluma 2000 6.5%, and for the self-etch systems ART 3.2%, Denthesive 2 5.7% and PUB 3 4.5% CONCLUSION: A continuous degradation of the resin-dentin bond was observed for all bonding systems during the follow-up expressed by the increasing loss rates. A wide variation of dentin bonding effectiveness was seen between the systems independent to adhesion strategy.

Acid Etching, Dental↗

PubMed2004

Effect of remaining demineralised dentine on dental microleakage accessed by a dye penetration: how to inhibit microleakage?

OBJECTIVES: To demonstrate that microleakage has taken place at the defect, which was analysed previously by a tensile test using dumbbell shaped specimens trimmed from bonded resin/dentine restorations, and to suggest how microleakage can be inhibited reliably in dental treatment. METHODS: A total of 60 Class V box cavities were prepared at the cemento-enamel junction on fresh bovine incisors and randomly divided into four groups of 15 specimens each. Exposure times of etching for 10:3 conditioner were set at 10, 30 or 60 s, and for 10% phosphoric acid (positive control) at 10 s. The cavity walls were rinsed with water for 10 s, air-dried for 10 s and hybridised with 4-META/MMA-TBB resin. All the cavities were filled with a light cured resin composite and stored in 37 degrees C water for 24 h and then immersed in 15% methylene blue for 2 h. The length of dye penetration along the interface was graded by defined criteria and analysed using Kruskal-Wallis and Mann-Whitney tests. The dye penetration patterns were examined by light microscopy and the remaining demineralised dentine was analysed by Transmission Electron Microscopy (TEM). RESULTS: The least leakage score was obtained in 10s-10:3 etched group with 12 out of 15 specimens demonstrating no leakage. Leakage was significantly lower at the cementum margin than for the other three groups. No significant difference in the extent of greatest dye penetration was found between the 60s-10:3 and 10s-phosphoric etched groups. Dye penetration along the cementum margins was significantly higher than that of the enamel margins in all groups, except the 10s-10:3 etched group. TEM examination confirmed that there were exposed collagen fibrils in the remaining demineralised dentine, where microleakage had taken place. SIGNIFICANCE: It could be concluded from this study that microleakage has taken place at the defect in the bonded specimens which has correlations with zones of incompletely infiltrated demineralised dentine that was observed using TEM. A reliable method of inhibiting microleakage is the presence of well prepared hybridised dentine.

Acid Etching, Dental↗

PubMed2004

Cuspal movement and microleakage in premolar teeth restored with posterior filling materials of varying reported volumetric shrinkage values.

OBJECTIVES: To investigate the effect of polymerisation shrinkage stress of various aesthetic posterior filling materials on cuspal movement and cervical gingival microleakage of mesio-occlusal-distal (MOD) restorations placed in increments in extracted maxillary premolar teeth. METHODS: Forty sound extracted upper premolar teeth were subjected to standardised preparation of a large MOD cavity. One curing regimen was used and each posterior filling material was placed in eight increments with the appropriate bonding system. A twin channel deflection-measuring gauge allowed a measurement of individual cusp deflections at each stage of polymerisation. Restored teeth were thermocycled before immersion in 0.2% basic fuchsin dye for 24h. After sagittal sectioning of the restored teeth in a mesio-distal plane, the sectioned restorations were examined to assess cervical gingival microleakage. RESULTS: In general, cuspal deflection measurements were dependent upon the constituent monomers and the associated shrinkage on curing, with significantly increased cuspal movement (P<0.05) being recorded for Z100 (20.03+/-2.92 microm) compared with Filtek Z250 (12.34+/-2.18 microm), P60 (13.41+/-4.43 microm) and Admira (11.2+/-2.58 microm). No significant differences were identified between the posterior filling materials when the cervical gingival microleakage scores were examined. CONCLUSIONS: It would appear that a reduction in the manufacturers' reported volumetric polymerisation shrinkage for Z100 (4.0%) to below 3% for Filtek Z250, P60 and Admira, resulted in a significant reduction in the associated cuspal strain on the MOD cavity. The diluent triethyleneglycol dimethacrylate (TEGDMA) increases the polymerisation shrinkage of Z100 resin-based composite due to an increased concentration of carbon-to-carbon double bonds (CC). The replacement of TEGDMA with urethane dimethacrylate (UDMA) and Bis-EMA in Filtek Z250 and P60, decreases the polymerisation shrinkage stress by increasing the cross-linking of polymer networks. However, no group was identified as producing less gingival microleakage at the cervical dentine cavosurface margin when the cavities were sectioned and examined, regardless of the reported variations in cuspal strain and the associated volumetric polymerisation shrinkage values.

Bicuspid↗

PubMed2005

Retention of a resin-modified glass ionomer adhesive in non-carious cervical lesions. A 6-year follow-up.

OBJECTIVES: The purpose of this study was to evaluate the clinical retention of a new resin-modified glass ionomer cement based adhesive combined with a hybrid resin composite or a poly-acid modified resin composite in non-carious cervical lesions during a 6-year period. METHODS: The resin-modified glass ionomer adhesive (Fuji Bond LC), was placed in 73 cervical lesions, 36 with a universal hybrid resin composite (Tetric Ceram) and 37 with a poly-acid modified resin composite (Hytac). Fifty-one in lesions with sclerotic dentin and 22 in non-sclerotic ones. Of the sclerotic lesions 38 were slightly roughened with a diamond bur before conditioning. The restorations were evaluated with slightly modified USPHS criteria every six months during a 6-year period. RESULTS: All except six restorations were evaluated during the 6 years. Twelve (17.9%) were lost, four Tetric Ceram (11.8%) and eight Hytac (24.2%) (p<0.05). Four were found in non-sclerotic lesions (20.0%) and eight in sclerotic lesions (17.0%). The differences between the sclerotic and non-sclerotic and the roughened and non-roughened lesions were not significant. CONCLUSIONS: The resin-modified glass adhesive showed a superior clinical retention combined with the resin composite material, with an annual failure rate of 2%.

Adult↗

PubMed2005

Cervical microleakage in composite restorations of primary teeth--in vitro study.

OBJECTIVE: The purpose of this study is to evaluate in vitro the cervical microleakage of two bonding systems (Group 1: Scotchbond Multi-Purpose-3M; Group 2: Clearfil Mega Bond-Kuraray) in occluso-proximal composite restorations of primary molars. METHODS: Two occluso-proximal standard cavities preparations (vertical slots) were made in each one of the 11 primary molars. The cavities were filled using adhesive systems (one for each cavity) and hybrid composite (Filtek Z250-3M) by incremental technique. The first increment was inserted horizontally at the cervical wall and light-cured with 100 mW/cm2 intensity for 60 s (VIP-Bisco). Other two increments were inserted diagonally on the buccal and lingual portion and each one light-cured with 200 mW/cm2 intensity for 60s. The restorations were finished and polished, and then partially sealed and embedded in 0.5% methylene blue solution for 24 h. The specimens were sectioned mesio-distally and the dye penetration was evaluated (score from 0 to 3) under a stereomicroscope. RESULTS: The statistical analysis (Qui square and Mann-Whitney non-parametric test) revealed no statistical difference (p=0.193) between the two adhesive systems tested. CONCLUSIONS: Both bonding systems provided small early cervical microleakage in occluso-proximal restorations of primary molars.

Coloring Agents↗

PubMed2006

Complicated root canal morphology of mandibular first premolar in a Chinese population using the cross section method.

The purpose of this study was to assess the canal anatomy and morphology of mandibular first premolars in a Chinese population. Eighty-two extracted mandibular first premolars with intact roots were collected and stored in a glutaraldehyde solution. The teeth were embedded in clear resin and the root length was measured. The roots were resected perpendicular to the long axis at 3, 6, 9, and 12 mm from the apex. The resected root surfaces were polished, rinsed, dried, and stained with methylene blue. Digital photographs of the cross-sectional root surfaces were made at 24X. The incidence of multiple canals and varied morphology was determined by two independent examiners. The results indicated that 54% of the mandibular first premolars demonstrated a single canal. Twenty-two percent contained two canals and 18% percent had C-shaped configuration. The C-shaped root canal occurred predominantly in the 3 and 6 mm sections with one or two canals coronally. A unique finding was the circumferential canal (apical delta), which was characterized by a single canal splitting into 3 or 4 canals. The incidence of circumferential canal was 6% and occurred only in the apical 3 mm cross-sections. Identification of this unique apical canal configuration and the high incidence of multiple canals in mandibular first premolars may explain endodontic treatment failure in this tooth group.

Anatomy, Cross-Sectional↗

PubMed2004

Spatial distribution of lead in the roots of human primary teeth.

Lead remains one of the most hazardous metals in our environment. The concentrations of lead in coronal dentine and enamel have previously been reported but limited information is available regarding lead levels in radicular dentine and cementum. This study reports the distribution of lead in 26 roots of 16 human maxillary primary teeth from seven individuals. In addition, calcium and phosphorous concentrations were also measured to detect any variations in the degree of mineralization in different regions of the roots. The mean lead concentration in these roots was 1.67 +/- 1.43 microg/g, which is comparable to other studies. In all cases there were higher lead concentrations in the apices of non-resorbed roots of primary maxillary teeth relative to middle and cervical regions. The findings reported here are of potential significance during the process of physiological root resorption whence periapical tissue may be exposed to higher levels of lead.

Calcium↗

PubMed2003

Finite element analysis of stresses in molars during clenching and mastication.

STATEMENT OF PROBLEM: During physiological functions of the masticatory system such as swallowing and chewing, teeth are subjected to variations in force application. Most in vitro analyses of stress have not analyzed the combined forces acting on teeth. PURPOSE: The purpose of this study was to analyze the stresses induced in a mandibular molar during clenching and chewing of morsels with various elastic moduli. MATERIALS AND METHODS: The investigation was performed by means of finite element analysis with the use of contact elements. Two-dimensional models of the mandibular first molar and the crown of the opposing maxillary molar were created. The computerized simulation evaluated the clenching and chewing of 4 morsels with different elastic moduli (similar to hard gum, tough meat, bone, and combination of hard gum and bone). The movement of the studied teeth was simulated in the frontal plane. Teeth models crushed morsels and closed into the maximal intercuspation position. The values of stresses in the mandibular molar were calculated during these situations. RESULTS: The study revealed that clenching of molars and chewing morsels of high elastic moduli resulted in maximal equivalent stresses within occlusal enamel. During mastication of morsels of low elastic moduli the stress concentration was located in the cervical region of the lingual side of the mandibular molar. Masticating a low-elasticity morsel containing a fragment of bone caused the highest equivalent stresses in the lingual wall and high tensile stresses in enamel near the central intercuspal fissure of the tooth studied. CONCLUSION: During mastication of various morsels, maximal equivalent stresses occurred in occlusal enamel and in the cervical region of the lingual wall of the first mandibular molar. The more unfavorable and highest stresses were exerted during mastication of nonhomogeneous morsels.

Bite Force↗

PubMed2005

In vivo correlation of noncarious cervical lesions and occlusal wear.

STATEMENT OF PROBLEM: The etiology of noncarious cervical lesions is not well understood. An understanding of the etiology helps the clinician determine appropriate treatment and management strategies. Purpose This study evaluated the relationship between noncarious cervical lesions and occlusal (or incisal) wear. MATERIAL AND METHODS: Casts (n = 299) made from dental students were articulated in a semi-adjustable articulator and evaluated. Data included the presence and contour of noncarious cervical lesions (NCLs) and the presence, location, and severity of any occlusal/incisal wear facets. Also included were Angle's classification, occlusal guidance patterns, midline, presence of tori, tooth restoration, reverse articulation (crossbite), open occlusal relationship, and posterior excursive contacts where present. Following a calibration procedure, 2 evaluators made independent observations on the casts. The first evaluator recorded for each tooth in each subject: presence and severity of NCLs, presence and extent of occlusal/proximal restorations, and presence of reverse articulation and open occlusal relationship. Following the first evaluation red rope wax was placed at the cervical margins of each tooth for the purpose of blinding the second evaluator from NCL observations. The second evaluator recorded severity and location of occlusal/incisal wear, presence or absence of posterior excursive contacts, Angle's classification, occlusal guidance pattern, any midline discrepancy, and presence or absence of tori. The Spearman correlation coefficient and chi 2 tests were used to analyze the data (alpha=.05). RESULTS: There was no relationship between noncarious cervical lesions and occlusal/incisal wear. There was also no correlation between NCLs and other parameters examined. CONCLUSIONS: Under the conditions of this study, noncarious cervical lesions are not related to occlusal wear.

Adult↗

PubMed2005

Long-term monitoring of microleakage of different amalgams with different liners.

STATEMENT OF PROBLEM: Microleakage is a major factor contributing to the occurrence of secondary caries around amalgam restorations. Purpose The purpose of this study was to evaluate the effect of amalgam type, liner type, and storage period on microleakage. MATERIAL AND METHODS: Two hundred seventy bovine incisors were divided into 18 groups (n = 15). Two high-copper amalgam alloys (admixed and spherical type) and 3 liner options (no liner, varnish, and adhesive) were used to restore Class V preparations. After placement of restorations, the teeth were stored for 3 different periods (1 day, 1 week, and 12 months) in saline solution, After storage, the specimens were immersed in 0.5% methylene blue for 24 hours, sectioned, and then mean depth of dye penetration was measured separately for the incisal and cervical areas with the use of a binocular microscope (x200). Scores were assigned to a millimeter scale (+/- 0.2 mm). The data were analyzed with a 3-way analysis of variance and the Tukey Honestly Significant Different test (alpha = .05). RESULTS: The 3-way interaction was significant (P < .001 for the cervical and occlusal margins). After short-term storage (1 day and 1 week), the admixed alloy showed significantly lower leakage values than the spherical alloy only in cervical margins (1.45 and 1.56 for the admixed and 1.62 and 1.50 for the spherical alloy at the cervical [P = .034] and incisal margins [P = .702]), respectively. After 12 months, values decreased significantly for both amalgams, which were similar and lower than for the short-term storage period (short-term values of 1.62 and 1.39 for the admixed and 1.69 and 1.46 for the spherical alloy at the cervical and incisal margins, respectively; long-term values of 0.22 and 0.20 for the admixed and 0.33 and 0.36 for the spherical alloy at the cervical and incisal margins, respectively [P < .019]). When the adhesive was used, significantly superior sealing was observed for both amalgams. For the no liner and cavity varnish groups, the admixed alloy showed superior performance compared to the spherical alloy (with no liner, 1.11 and 0.98 for the admixed and 0.83 and 1.08 for the spherical alloy at the cervical and incisal margins, respectively; with varnish, 1.19 and 1.22 for the admixed and 1.63 and 1.34 for the spherical alloy, at the cervical and incisal margins, respectively [P < .037]). CONCLUSION: In the short-term, the lowest degree of leakage was found when adhesive was used. After 1 year, no differences were detected, regardless of the amalgam type and liner used.

Analysis of Variance↗

PubMed2005

Fracture resistance of endodontically treated maxillary premolars restored with CAD/CAM ceramic inlays.

STATEMENT OF PROBLEM: Endodontically treated posterior teeth are more likely to fracture compared to posterior teeth with vital pulps. Reinforcement with an extracoronal restoration that covers the cusps is the most commonly recommended method for reducing the risk of fracture. It is not known whether bonded intracoronal restorations without cuspal coverage will reduce the risk of fracture. PURPOSE: The aim of this in vitro study was to investigate whether reinforcement of endodontically treated premolars with MOD preparations could be achieved by insertion of bonded CAD/CAM ceramic inlays. MATERIAL AND METHODS: Forty-five extracted maxillary premolars were equally distributed among 3 groups (END, CER, CTR). In group END (n=15), root canals were enlarged with a rotary NiTi system and obturated with heat-softened gutta-percha around a plastic carrier (Thermafil). After filling of the endodontic access cavities with autopolymerizing composite resin (Luxacore), standardized MOD cavity preparations were made and CAD/CAM ceramic inlays (CEREC) were fabricated and then bonded to the teeth with composite resin (Tetric) and an adhesive system (Syntac Classic). In group CER (n=15), teeth without endodontic treatment were restored with bonded inlays (CEREC). Sound premolars served as controls (group CTR, n=15). Teeth were then thermal cycled (1445 cycles, dwell time: 30 seconds, 5 degrees /55 degrees C). An eccentric load was applied on the buccal incline of the palatal cusp in a universal testing machine until cusp fracture (N). Fracture load was evaluated with the Mann-Whitney test, and type of fracture, with a chi-square analysis (alpha=.05). The type of fracture was determined by visual inspection: type I - supragingival fracture within the palatal cusp; type II - fracture below cemento-enamel junction of palatal cusp; and type III - fracture of palatal cusp and central portion of the tooth exposing the root canal cavity. RESULTS: No significant difference was found among the 3 groups with respect to load required for fracture. Mean fracture load +/- SD was recorded as follows: 291.6 +/- 113.7 N for group END, 363.2 +/- 140.3 N for group CER, and 296.5 +/- 170.5 N for group CTR. Regarding fracture modes, significantly more teeth from group END exhibited fractures of type III and II compared with control specimens. CONCLUSION: Teeth restored with bonded CAD/CAM ceramic inlays (CEREC) fractured with a significantly higher number of severe fractures compared to the control group.

Bicuspid↗

PubMed2005

Age-related changes in tooth enamel as measured by electron microscopy: implications for porcelain laminate veneers.

STATEMENT OF PROBLEM: Available information on the dimensions of the enamel and pulp tissues of tooth structure, as well as their correlation with chronologic age, is limited. However, this information is a significant determinate in planning the tooth reduction for a porcelain laminate veneer (PLV) restoration. PURPOSE: This study examined variations in tooth enamel thickness and its correlation with chronologic age as it relates to available tooth substrate for PLV restorations. MATERIAL AND METHODS: Forty human maxillary central incisors extracted from patients within the age range of 30 to 69 years were used to evaluate the thickness of tooth layers. Measurements were made for the following tooth areas using scanning electron microscopy (SEM): facial enamel thickness at 1, 3, and 5 mm above the cemento-enamel junction (CEJ), palatal enamel thickness at 5 mm above the CEJ, facial and palatal enamel thickness at the incisal edge, maximum facial-palatal (MFP) width at incisal edge, physiologic secondary dentin (PSD) height, facial-cervical enamel-pulp (FCEP) distance, and the incisal edge enamel-pulp (IEP) distance. The relationship between thickness and age was evaluated with a regression analysis (alpha=.05). RESULTS: Significant differences (P<.001) were observed in all of the relationships between tooth thicknesses and chronological age. Outcome variables of enamel thickness related to age showed a steady decrease, beginning at approximately age 50. Mean values of facial enamel thickness at 1, 3, and 5 mm above the CEJ were 0.31 +/- 0.01, 0.54 +/- 0.01, and 0.75 +/- 0.02 mm, respectively, for the age range of 30 to 69 years. The thickness of maximum incisal width (R(2) = 0.95), PSD height (R(2) = 0.76), and IEP distance (R(2) = 0.99) indicated that all are subject to an increase in relation to age. CONCLUSION: Facial enamel thickness above the CEJ decreases, while MFP increases in relation to age. The PSD height and IEP distance also increased with age.

Adult↗

PubMed1998

A scanning electron-microscopic study of developing human deciduous enamel on the dependence of the outline of surface pits on the angle of observation.

On the developing enamel surfaces of fetal human deciduous teeth, many of the surface pits were arcade-shaped with the arcade preferentially pointing in a cervical direction. The configuration of the interprism ridges between the pits contributed to this appearance. Surface cracks allowed verification of an incisal inclination of the subsurface prisms. This apparent paradox was solved when the specimens were tilted so that the pits were viewed in the directions of the prisms, giving the pits a compressed arcade-shape with the arcades pointing incisally. It is recommended that care should be exercised and due attention paid to the angle of observation when determining the orientation of pit arcades. Pit entry direction seems to be a more reliable feature for inferring the direction of tangential ameloblast movement.

Ameloblasts↗

PubMed1997

Root reinforcement with a resin-bonded preformed post.

PURPOSE: This study evaluated the ability of resin-bonded posts to reinforce teeth that are structurally weak in the cervical area against fracture. MATERIAL AND METHODS: Forty canine roots were endodontically treated and randomly distributed into four groups of 10. Parallel-sided preformed posts were cemented into the roots of these teeth after their crowns were removed. The cervical third of the canals were flared to simulate teeth weakened in this area as a result of caries or endodontic therapy. Three resin cements and a zine-phosphate cement, which was used as the control, were used to secure the posts into the roots. Cemented posts were loaded in an Instron testing machine with a gradually increasing force at a 60-degree angle to the long axis of the root until the root fractured. RESULTS: Roots in which the posts were cemented with Panavia were significantly more resistant to fracture than those where zinc phosphate was used (p < 0.05). Because of the inability to determine exactly the point of failure of the zinc-phosphate cement, no statistically significant difference was found when compared with the other two resin cements (ANOVA and Student-Newman-Keuls test).

Analysis of Variance↗