Search

Objectives: The purpose of this study was to investigate the effect of tooth age on colour adjustment potential of resin composite restorations in human teeth., Methods: Twenty extracted human premolars with an A2 shade, extracted for orthodontic reasons from younger patients (20-28yrs) (younger teeth) and periodontal reasons from older patients (45-69yrs) (older teeth), were used in this study. Cylindrical shaped cavities (3.0mm depth; 2.0mm diameter) were prepared in the centre of the crowns on the buccal surface. One of four resin composites of A2 shade (Kalore, KA; Solare, SO; Clearfil Majesty, MJ; Beautifil II, BF) was placed in the cavity, and the colour was measured at four areas (0.4mm×0.4mm) on the restored teeth (area 1; tooth area 1.0mm away from the border of resin composite restoration: area 2; tooth border area 0.3mm away from margin of resin composite restoration: area 3; resin composite border area 0.3mm away from margin of resin composite restoration: area 4; resin composite area at the centre of resin composite restoration) using a spectrophotometer (Crystaleye). The colour of each area was determined according to the CIELAB colour scale. Colour differences (ΔE*) between the areas of 1 and 2, 2 and 3, 3 and 4 and 1 and 4 were calculated, and also the ratio of ΔE*area2-3 to ΔE*area1-4 (ΔE*area2-3/1-4), ΔE*area3-4 to ΔE*area1-4 (ΔE*area3-4/1-4) and ΔE*area1-2 to ΔE*area1-4 (ΔE*area1-2/1-4) as a parameter of the colour shift in resin composite restoration, were determined. Moreover, the light transmission characteristics of the resin materials and dentine discs from the younger and older teeth were measured using a goniophotometer. The data were statistically analyzed using two-way ANOVA, and Dunnett's T3 and t-test for the post hoc test., Results: ΔE*area2-3 (colour difference between resin composite and tooth at the border) and ΔE*area1-4 (colour difference between resin composite and tooth) of the older teeth groups were significantly larger than those of younger teeth groups (p<0.05). The ΔE*area2-3/1-4 (mis-match rate in colour shifting at the border) of the older teeth groups was larger than that of the younger teeth groups (p<0.05). ΔE*area3-4/1-4 (colour shifting rate of resin composite side) was significantly larger in older teeth than younger teeth (p<0.05), while ΔE*area1-2/1-4 (colour shifting rate of tooth side), was significantly smaller in older teeth than younger teeth (p<0.05). In each tooth group, there were no significant differences in ΔE*area2-3, ΔE*area1-4, ΔE*area2-3/1-4, ΔE*area3-4/1-4 and ΔE*area1-2/1-4 between the materials (p>0.05). Analysis of the light transmission properties indicated that older dentine transmitted more light, while younger dentine exhibited greater light diffusion and transmitted less light., Conclusions: The colour shifting effects at the border of the resin composite restorations were influenced by the age of the tooth. This behaviour might be influenced by the light transmission characteristics of dentine in restored teeth., Clinical Significance: The potential for colour adjustment of resin composite restorations may be less in older teeth than younger teeth., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Objectives: The aim of this study was to investigate the recovery of cuspal stiffness and fracture resistance in endodontically treated maxillary premolars restored with bonded ceramic inlays and onlays of various designs., Methods: Seventy intact premolars were selected for this study; six cavity designs were investigated: (i) mesio-occlusal-distal (MOD) inlay (I), (ii) MOD inlay with palatal cusp coverage (IPC), (iii) MOD onlay (O), (iv) MOD inlay with pulp chamber extension (IPE), (v) MOD inlay with palatal cusp coverage and pulp chamber extension (IPCPE), and (vi) MOD onlay with pulp chamber extension (OPE). Intact teeth acted as control. Strain gauges were attached to the buccal and palatal surfaces of the teeth to measure cuspal stiffness under static loading. All specimens were eventually subjected to compressive load to failure. Cuspal stiffness and fracture resistance data were analyzed using ANOVA and Tukey test., Results: The I and IPE restorations restored cuspal stiffness to 75% of the sound tooth value. The O and OPE restored teeth had stiffness values greater than that of a sound tooth. The I, IPC, O, IPE, IPCPE and OPE restored teeth demonstrated fracture strength values of 938N±113 N (s.d.), 1073N±176 N and 1317N±219 N, 893N±129 N, 1062N±153 N and 1347N±191 N respectively., Conclusions: Within the limitations of this study, it was concluded that the all-ceramic onlay or inlay with palatal cusp coverage provided best biomechanical advantage in restoring an endodontically treated maxillary premolar tooth., Clinical Significance: The onlay approach which is more conservative compared to full coverage restoration is considered an appropriate approach to the restoration of endodontically treated maxillary premolars. The addition of a pulpal extension to the all-ceramic restorations, apart from being technically challenging, was not found to offer any biomechanical advantage to the restored teeth., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Objectives: To assess the adhesive performance of three universal bonding systems (self-etch and total-etch protocols) with cuspal deflection and cervical microleakage score., Methods: Fifty-six standardised sound maxillary premolar teeth with uniform mesio-occlusal-distal (MOD) cavities were randomly allocated to six groups. Restoration with resin-based composite (RBC) was performed in conjunction with a universal bonding system facilitated by a quartz-tungsten-halogen light-curing-unit. The dependent variable was the universal bonding protocol (self-etch or total-etch). Buccal and palatal cuspal deflections were recorded at 0, 30, 60 and 180s post-irradiation using a twin channel deflection measuring gauge. Following restoration, the teeth subjected to 500 thermocycles, immersed in a 0.2% basic fuchsin dye for 24h, sectioned and examined for cervical microleakage., Results: Comparing between bonding protocol (self-etch or total-etch), a decrease in total cuspal deflection and a concomitant increase in cervical microleakage were evident when employing the total-etch compared with the self-etch protocol for two of the three universal dental adhesives., Conclusions: The 'Adhesion-Decalcification concept' suggests a trend towards 'mild self-etch' adhesives. Differences in adhesive performance (cuspal deflection and cervical microleakage) between the teeth restored using the self-etch or total-etch protocols is suggested to be a result of the pH of the self-etch solutions. 'Mild self-etch' (pH∼2.0) adhesives out-performed ultra-mild (pH>2.5) or strong (pH<1.5) self-etch solutions., Clinical Significance: Poorly performing adhesives could be identified using the cuspal deflection and cervical microleakage protocol reported which could save the complications encountered clinically with Class II RBC restorations., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Objectives: To assess the cuspal deflection and cervical microleakage of standardised Class II cavities incrementally filled with a dimethacrylate RBC or bulk-fill flowable RBC bases., Methods: Twenty-four sound upper premolar teeth with Class II cavities were allocated to three groups (n=8). Restoration of the teeth involved the placement of an RBC (GrandioSO) in eight oblique increments (Group A) or Groups B and C were restored to within 2 mm of the palatal cusp in a single increment with bulk-fill flowable RBC bases (SDR and x-tra base) before the two occlusal cavity increments were placed with GrandioSO. Buccal and palatal cusp deflections were recorded postirradiation using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in 0.2% basic fuchsin dye for 24h, sectioned and examined for cervical microleakage., Results: The mean total cuspal deflection for the oblique incremental restoration technique was 11.26 (2.56) μm (Group A) and 4.63 (1.19) μm (Group B) and 4.73 (0.99) μm (Group C) for the bulk-fill flowable RBC bases. A significant increase in the mean total cuspal deflection for the incrementally filled GrandioSO compared with the SDR (P=0.007) and x-tra base (P=0.005) restored teeth was evident. No significant difference in the cervical microleakage scores was recorded between groups AC (P>0.05)., Conclusions: The bulk-fill flowable RBC bases significantly reduced cuspal deflection compared with a conventional RBC restored in an oblique incremental filling technique with no associated change in cervical microleakage recorded., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Objectives: The purpose of this study was to establish the factors influencing the masticatory performance of older subjects with varying degrees of tooth loss and associated numbers of posterior occlusal contacts., Methods: The subjects consisted of 1274 independently living people aged 60 years and over. Individuals with partially or fully edentulous arches without a denture replacement or those having any symptoms related to an oral problem were excluded from the study participants. Masticatory performance, maximal occlusal force and stimulated whole saliva were measured. Subjects were grouped into three categories by posterior occlusal contact, according to the Eichner Index. Group A had contacts in four support zones; group B had one to three zones of contact or contact in the anterior region only; and group C had no support zones at all, although a few teeth could still remain., Results: The masticatory performance in groups B and C was found to be 81% and 50% of that of group A, respectively. The multiple linear regression analysis showed that in all the groups, occlusal force was significantly associated with masticatory performance. In groups A and B, the number of residual teeth was significantly associated with masticatory performance, whereas in group C, it had no significant relationship with masticatory performance. Salivary flow rate had a significant correlation with masticatory performance only in group C., Conclusions: Declines in occlusal contact, occlusal force and salivary flow appear to be associated with reduction of masticatory performance in older adults. However, the crucial factors for masticatory performance varied, depending on the phase of occlusal collapse., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Objectives: The aim of the present work is to investigate the effects of cementum-dentine junction (CDJ) and cementum on the stress distribution in the periodontal ligament (PDL) and alveolar bone., Methods: Based on the anatomical profiles and the recently reported theories about the tooth attachment mechanism, the finite element (FE) model of a mandibular second premolar along with its detailed supporting structures was developed. The effect of CDJ and cementum was evaluated by comparing the resulting stresses of FE models of the second mandibular premolar with and without CDJ and cementum in tooth supporting structure., Results: The stress levels are higher in the structure without CDJ and cementum than that with CDJ and cementum. The function of CDJ and cementum is as a cushion pad decreasing the stress in the PDL and alveolar bone under loading., Conclusions: As a major result of this study, it can be concluded that the CDJ and cementum significantly influence the stress distribution within the tooth supporting structure. However, most of the reported FE analysis did not take CDJ and cementum into account, which possibly resulted in overestimated stress values in the PDL and alveolar bone. From a bio-engineering perspective, the results of this study provide guidance for the design of dental implants and the application of orthodontic force system as well., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Objectives: The purpose of this study was to determine the influence of the occlusal rest position in removable partial dentures on the displacement of the abutment tooth and the stress distribution in the periodontal ligament (PL)., Methods: We constructed three-dimensional finite element models of the mandibular first and second premolars. A layer of the PL and a mesial or distal occlusal rest were produced on the second premolar as an abutment. A zero displacement was prescribed on the outer surface of the PL and the first premolar. In each simulation, the rest was moved 0.05 mm vertically to the apical direction, with or without restriction of horizontal movements. We simulated the contact phenomena on the abutment surfaces, and calculated the movements of the abutment and stress distributions in the PL., Results: We observed a maximum distal displacement of 42 microm at the buccal cusp of the abutment and a principal compressive stress of 0.35 MPa in the PL when the abutment was vertically loaded by a distal rest that was allowed to move horizontally. However, the displacements and stresses were relatively small, and were all within the physiological limitations of the tissues. The restriction of the horizontal movement of the rests was effective in reducing the horizontal displacements of the abutment, regardless of the rest position., Conclusions: The single vertical load exerted from either the mesial or distal rest on the abutment was unlikely to cause any mechanical damage to its supporting tissues.

Objectives: The objective of this study was to use a three-dimensional (3-D) finite element model to investigate normal stress distribution to substantiate the tooth flexure mechanism. The study also compared the changes in the stresses by different occlusal loading sites and directions., Methods: The 3-D finite element analysis was used. A maxillary premolar was selected to construct the simulation model. The model was constructed step-by-step for convergence and validity. Seven load conditions for various load sites and different directions were simulated to the model., Results: The maximal principal stress and minimal principal stress distributions developed within the structures of seven load conditions were output and their stress distributions on z-plane at the vertical midline were shown. The peak tensile stress of the cervical area for various load conditions were compared and listed., Conclusions: This study has shown that the presence of tensile stresses in the cervical region of a maxillary premolar by various loading sites and different directions. The results coincided with the stress-induced theory, hence sustaining it. The relationship of the affected factors of leverage to the development of cervical abfraction lesions, was explored., (Copyright 2002 Elsevier Science Ltd.)

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.