Inhibition of bacterial growth on zirconia abutment with a helium cold atmospheric plasma jet treatment.

OBJECTIVES: This study presents a surface modification method to treat the zirconia implant abutment materials using a helium cold atmospheric plasma (CAP) jet in order to evaluate its efficacy on oral bacteria adhesion and growth. MATERIALS AND METHODS: Yttrium-Stabilized Zirconia disks were subjected to helium CAP treatment; after the treatment, zirconia surface was evaluated using scanning electron microscopy, a contact angle measuring device, X-ray photoelectron spectroscopy for surface characteristics. The response of Streptococcus mutans and Porphyromonas gingivalis on treated surface was evaluated by a scanning electron microscopy, MTT assay, and LIVE/DEAD staining. The biofilm formation was analyzed using a crystal violet assay. RESULTS: After the helium CAP jet treatment, the zirconia surface chemistry has been changed while the surface topography remains unchanged, the bacterial growth was inhibited, and the biofilm forming decreased. As the treatment time increases, the zirconia abutment showed a better bacterial inhibition efficacy. CONCLUSIONS: The helium CAP jet surface modification approach can eliminate bacterial growth on zirconia surface with surface chemistry change, while surface topography remained. CLINICAL RELEVANCE: Soft tissue seal around dental implant abutment plays a crucial role in maintaining long-term success. However, it is weaker than periodontal barriers and vulnerable to bacterial invasion. CAP has a potential prospect for improving soft tissue seal around the zirconia abutment, therefore providing better esthetics and most of all, prevent peri-implant lesions from happening.

[Effect of different cleaning methods on bond strength and surface wettability of high translucency zirconia].

PURPOSE: To study the effect of different cleaning methods on the shear bond strength of self-adhesive resin cement to saliva-contaminated high translucency zirconia and surface wettability. METHODS: Eighty zirconia specimens were randomly divided into 5 groups (n=16), i.e., control group(not contaminated), 75% ethanol group,cleaning paste group,airborne-particle abrasion group, and atmospheric pressure cold plasma group. The contact angles was measured, shear bond strength were examined, and fracture types were determined. SPSS 26.0 software package was used for statistical analysis of the data. RESULTS: The atmospheric pressure cold plasma group produced the lowest contact angle(P＜0.05). The shear bond strength of the airborne-particle abrasion group, the cleaning paste group and the atmospheric pressure cold plasma group respectively were similar to the control group without significant difference(P＞0.05), while those were significantly higher than 75% ethanol group(P＜0.05). The mixed fracture mode of the atmospheric pressure cold plasma group evidently increased. CONCLUSIONS: Airborne-particle abrasion, cleaning paste and atmospheric pressure cold plasma overcome the effects of saliva contamination, producing the shear bond strength to zirconia similar to the control group. The atmospheric pressure cold plasma improves hydrophilicity of high translucency zirconia significantly.

[Effect of Shofu gingival matrices which simulate the gingival color on spectrophotometric tooth color measurement].

OBJECTIVE: To investigate the effect of gingival color on spectrophotometric color measurement in a standardized model. METHODS: Shofu gingival matrices were used to simulate the soft tissue and VITA Classical shade tabs were fixed into them. Both the gingival matrices and shade tabs were measured with Crystaleye spectrophotometer in a black box. Regions of the shade tabs, gingival color and their combinated effect on measurements were analyzed, Pearson correlation analysis was used to identify the correlation of the gingival color difference with the shade tabs color difference. RESULTS: The ranges of color difference were 1.01-2.26 in the cervical, 0.93-1.27 in the body and 1.67-2.97 in the incisal regions, respectively. Statistical analysis revealed that there was significant difference among all the gingival groups in the cervical region. Color differences were similar in the body and the incisal regions. The color measurement with Crystaleye was influenced by the regions of the shade tabs, the gingival color and their combination (P<0.001). Pearson Correlation Coefficient was 0.646 in the cervical, 0.386 in the body and 0.217 in the incisal regions respectively(P<0.001). CONCLUSION: The color measurement in the cervical region with the spectrophotometer was influenced by the color of the simulated gingiva. Such influence was not obvious in the body and incisal regions. Color coordinates changed regularly with the gingival color.

[Precision and accuracy of a dental spectrophotometer in gingival color measurement of maxillary anterior gingival].

OBJECTIVE: To explore a gingival shade matching method and to evaluate the precision and accuracy of a dental spectrophotometer modified to be used in gingival color measurement. METHODS: Crystaleye, a dental spectrophotometer (Olympus, Tokyo, Japan) with a custom shading cover was tested. For precision assessment, two experienced experimenters measured anterior maxillary incisors five times for each tooth. A total of 20 healthy gingival sites (attached gingiva, free gingiva and medial gingival papilla in anterior maxillary region) were measured,the Commission Internationale de I' Eclairage (CIE) color parameters (CIE L*a*b*) of which were analyzed using the supporting software. For accuracy assessment, a rectangular area of approximately 3 mm×3 mm was chosen in the attached gingival portion for spectral analysis. PR715 (SpectraScan;Photo Research Inc.,California, USA), a spectroradiometer, was utilized as standard control. Average color differences (ΔE) between the values from PR715 and Crystaleye were calculated. RESULTS: In precision assessment,ΔL* between the values in all the test sites and average values were from(0.28±0.16)to(0.78±0.57), with Δa*and Δb* from(0.28±0.15)to (0.87±0.65),from(0.19±0.09)to( 0.58±0.78), respectively. Average ΔE between values in all test sites and average values were from (0.62 ± 0.17) to (1.25 ± 0.98) CIELAB units, with a total average ΔE(0.90 ± 0.18). In accuracy assessment, ΔL* with control device were from(0.58±0.50)to(2.22±1.89),with Δa*and Δb* from(1.03±0.67)to(2.99±1.32),from(0.68±0.78)to(1.26±0.83), respectively. Average ΔE with the control device were from (2.44±0.82) to (3.51±1.03) CIELAB units, with a total average ΔE (2.96 ± 1.08). CONCLUSION: With appropriate modification, Crystaleye, the spectrophotometer, has demonstrated relative minor color variations that can be useful in gingival color measurement.

Effect of multiple coatings of one-step self-etching adhesive on microtensile bond strength to primary dentin.

OBJECTIVE: To investigate the effect of multiple coatings of the one-step self-etching adhesive on immediate microtensile bond strength to primary dentin. METHODS: Twelve caries-free human primary molars were randomly divided into 2 groups with 6 teeth each. In group 1, each tooth was hemisected into two halves. One half was assigned to control subgroup 1, which was bonded with a single-step self-etching adhesive according to the manufacturer's instructions; the other half was assigned to experimental subgroup 1 in which the adhesive was applied three times before light curing. In group 2, the teeth were also hemisected into two halves. One half was assigned to control subgroup 2, which was bonded with the single-step self-etching adhesive according to the manufacturer's instructions; the other half was assigned to experimental subgroup 2 in which three layers of adhesive were applied with light curing each successive layer. Microtensile bond strength was immediately tested after specimen preparation. RESULTS: When the adhesive was applied three times before light curing, the bond strength of the experimental subgroup 1 (n=33, 57.49 +/-11.61 MPa) was higher than that of the control subgroup 1 (n=31, 49.71 +/-11.43 MPa, P<0.05). When using the technique of applying multiple layers of adhesive with light curing each successive layer, no difference of immediate bond strength was observed between the control subgroup 2 and the experimental subgroup 2 (P>0.05). CONCLUSION: strength to primary dentin when using the technique of light-curing after applying three layers of adhesive.

[H(2)O(2) treatment improves the bond strength between glass fiber posts and resin cement].

OBJECTIVE: To evaluate the effect of etching with H2O2 on the bond strength between epoxy-based glass fiber posts and resin cement. METHODS: Sixteen epoxy-based glass fiber posts were randomly divided into 4 groups (4 posts in each group) for different surface treatments. Group 1, no surface treatment (Control group); Group 2, treated with silane coupling agent for 60 s; Group 3, immersed in 10% H2O2 for 10 min then treated with silane coupling agent for 60 s; Group 4, immersed in 30% H2O2 for 10 min then treated with silane coupling agent for 60 s. Resin cement was used for the post cementation to form resin slabs which were then sectioned and trimmed into dumbbell shape to obtain microtensile specimens. Microtensile bond strengths were tested and the failure modes were examined with a stereomicroscope. Statistical analysis of microtensile bond strengths was performed with Kruskal-Wallis test. RESULTS: The microtensile bond strengths (standard deviation) were 18.81 (4.04) MPa for Group 1, 26.70 (9.63) MPa for Group 2, 39.07 (6.47) MPa for Group 3, 46.05 (5.97) MPa for Group 4. CONCLUSION: Etching with H2O2 followed by silanization could significantly improve the bond strength between epoxy-based glass fiber posts and resin cement.

Evaluation of Newly Developed Double-layer Composite Resin Teeth for Crown Preparation Training.

OBJECTIVE: To evaluate and compare the crown preparation performance of preclinical dental students training with conventional composite resin teeth and newly developed double-layer composite resin teeth. METHODS: The newly developed composite resin teeth consisted of two layers with different colours and hardnesses. Twenty third-year undergraduate dental students (8 men, 12 women) were randomly assigned to the control group (Group 1, using conventional composite resin teeth; n = 10) or the experimental group (Group 2, using double-layer composite resin teeth; n = 10) to prepare metal-ceramic crowns. To practice, each student prepared one tooth per day for 2 days. For the baseline test and final test before and after the practice period, both groups used traditional teeth. The operation time was recorded and the prepared teeth were scored blindly by two experienced instructors. The time and scores were compared within and between groups to determine the difference (α = 0.05). RESULTS: Students in both groups spent less time (P < 0.05) and achieved better scores (P < 0.001) on the final test than the baseline test (P < 0.01). In the final test, no significant difference in operating time was found between the two groups (P > 0.05), but Group 2 yielded significantly higher scores (P < 0.05). CONCLUSION: Training with the double-layer composite resin teeth enabled students to progress more quickly in terms of operating time and achieve higher scores. Use of this newly-developed tooth in crown preparation teaching practice therefore yields highly promising results.

Time-dependent reactive oxygen species inhibit Streptococcus mutans growth on zirconia after a helium cold atmospheric plasma treatment.

As an efficient strategy for the modification of material surfaces, cold atmospheric plasma (CAP) has been used in dentistry to improve hard and soft tissue integration of dental implant materials. We previously found the Streptococcus mutans growth was inhibited on the surface of zirconia implant abutment after a 60-second helium cold atmospheric plasma treatment. However, the mechanism of bacterial growth inhibition on CAP-treated zirconia has not been fully understood. The duration of bacterial inhibition effectiveness on CAP-treated zirconia has also been insufficiently examined. In this work, we assume that reactive oxygen species (ROS) are the primary cause of bacterial inhibition on CAP-treated zirconia. The ROS staining and an ROS scavenger were utilized to evaluate the bacterial intracellular ROS level, and to determine the role of ROS in bacterial growth inhibition when seeded on CAP-treated zirconia. The time-dependent effectiveness of CAP treatment was determined by changes in surface characteristics and antibacterial efficacy of zirconia with different storage times after CAP treatment. This study confirmed that the presence of reactive oxygen species on the zirconia surface after CAP treatment inhibits the growth of Streptococcus mutans on the material surface. Although the antibacterial efficacy of the 60-second CAP-treated zirconia decreased over time, there were fewer bacteria on the treated surface than those on the untreated surface after 14 days.

[Clinical evaluation of denture made of pure titanium].

OBJECTIVE: To evaluate the clinical effect of pure titanium used for complete denture and removable partial denture. METHODS: Sixty edentulous patients were selected. Thirty patients in the test group for pure titanium denture and the other 30 in control for Co-Cr Alloy denture. RESULTS: No significant differences in clinical effect between dental casting pure titanium and casting Co-Cr alloy used for complete denture or removable partial denture. CONCLUSION: Due to the properties and biocompatibility, pure titanium can be used for denture base and frameworks of removable partial denture.

[Study on the correlation between the mandibular masticatory muscle movement and sleep tooth wear].

OBJECTIVE: To investigate the correlation between the clinical diagnostic criteria of sleep bruxism and the frequency of mandibular movements during sleep. METHODS: Video polysomnography was used to record 20 healthy adults with at least one of the following clinical symptoms and signs: 1) report of frequent tooth grinding; 2) tooth wear and dentin exposure with at least three occlusal surfaces; 3) masticatory muscle symptoms in the morning; 4) masseter muscle hypertrophy. The rhythmic masticatory muscle activity (RMMA) and isolated tonic activity were scored to compare the correlations with clinical symptoms and signs. Finally, the incidence of temporomandibular disorders (TMD) was investigated in patients with isolated tonic and RMMA subjects. RESULTS: Among the 20 subjects, RMMA events were observed (5.8±3.1) times·h⁻¹ and isolated tonic episodes were observed (2.1±0.9) times·h⁻¹. The frequency of RMMA events was significantly greater in the patients with acoustic molars than in those without (P<0.05). Similarly, the frequency of RMMA events was significantly greater in the patients with tooth attrition than in those without (P<0.05). However, no difference was observed between the occurrence of RMMA and the symptoms of masticatory muscles or masseter hypertrophy in the morning. The incidence of TMD was significantly higher in the patients with RMMA than in the isolated tonic patients. CONCLUSIONS: The clinical symptoms and signs often used to diagnose sleep bruxism are different clinical and physiological mandibular movements during sleep. RMMA during sleep can reflect the occurrence of tooth attrition and the high risk of TMD.

Demonstration of three injection methods for the analysis of extrinsic and intrinsic blood supply of the peripheral nerve.

BACKGROUND: The use of free vascularized nerve grafts requires an intimate and accurate knowledge of the blood supply of peripheral nerve. This study was designed to compare the advantages and disadvantages of three methods employed to reveal the blood supply of the peripheral nerve, and to provide morphological basis for vascularized nerve grafts. METHODS: The blood supply of brachial plexus and its main branches (ulnar, median, radial, musculocutaneous and axillary nerve) were observed using three vascular injection techniques: three specimens were injected with red latex through the thoracic aorta; two side specimens were injected with a Chinese ink solution, through the subclavian artery, for diaphanization and histology; one fresh cadaver was injected with the gelatin-lead oxide mixture through the femoral artery for radiography. RESULTS: The blood supply of the brachial plexus and its main branches was well examined using the three different vascular injection techniques. Perfusion with red latex exposed the extrinsic blood supply. Diaphanization and histology showed the intrinsic blood supply, while gelatin-lead oxide injection technique interactively displayed both the intrinsic and extrinsic blood supply to the peripheral nerve. CONCLUSION: The standard method for the study of the extrinsic blood supply to the peripheral nerve is the red latex perfusion; diaphanization and histology are very suitable to study the intrinsic blood supply of the peripheral nerve; while gelatin-lead oxide technique is the standard for visualization of the integral topography of the blood supply of the peripheral nerve.

Effect of Provisional Restorations with Ovate Pontics on Preservation of the Ridge after Tooth Extraction: Case Series.

OBJECTIVE: To evaluate the effect of provisional restorations using ovate pontics on the hard and soft tissues of the alveolar ridge after tooth extraction. METHODS: Patients with intact buccal bone after extraction of a maxillary incisor underwent a series of treatments. The protocol included tooth extraction and provisional restoration using ovate pontics. The outcomes were assessed 1, 3 and 6 months after the procedure, regarding changes in bone volume and soft tissue dimension. RESULTS: A total of 11 patients (6 female and 5 male) were treated using an ovate pontic provisional restoration after tooth extraction. After 6 months, bone loss at level 1, 3 and 5 mm below the most coronal section of the bone crest was 2.28 ± 0.53 mm, 1.51 ± 0.30 mm and 1.46 ± 0.41 mm, respectively. Changes in bone volume of these three levels were significantly lower (P < 0.01) than changes previously reported in the literature. The mesial and distal papillae recessed 0.47 ± 0.24 mm and 0.88 ± 0.57 mm, respectively, whereas the midfacial shrinkage was 0.86 ± 0.44 mm. The dimension of the ridge contour around the socket reduced mostly at 3 and 5 mm below the coronal section and the gingival mucosa, with values of 1.68 ± 0.48 mm and 1.61 ± 0.48 mm, respectively. CONCLUSION: Using a provisional restoration with ovate pontics after tooth extraction may preserve the alveolar ridge by sustaining the soft tissue, in particular the gingival papilla.

Effects of a modified cold atmospheric plasma jet treatment on resin-dentin bonding.

The radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma is a novel cold atmospheric plasma (CAP) source, which has low energy characteristic. This study investigated the effect of RF-APGD plasma on the mechanical properties of dentin collagen and resin-dentin bonding. The scanning electron microscopy analysis was performed before and after a novel RF-APGD plasma and a conventional CAP treatment and a tensile test was carried out for the stiffness of dentin collagen. The microtensile resin-dentin bond strength was tested either immediately or after a 50,000-cycle thermocycling process. Dentin collagen maintained an intact structure after a 45-s RF-APGD plasma treatment, whereas even a 10-s treatment with the conventional CAP collapsed the collagen scaffold. When compared with control groups, the RF-APGD plasma treatment showed: (i) an improved stiffness of dentin collagen; (ii) a significant improvement in the bonding strength before/after artificial aging. Thus, RF-APGD plasma treatment has excellent prospects as a resin-dentin bonding protocol.

[Stability of phonetics to determine the horizontal jaw relation in healthy adults].

OBJECTIVE: The aim of this study was to compare the mandibular position when speaking with the intercuspal position and to check the stability of phonetics when determining the horizontal jaw relation in healthy adults. METHODS: A total of 19 healthy volunteers were recruited. Seven Chinese letters, namely, /xi/, /er/, /yi/, /ci/, /mi/, /ni/, and /ri/, were chosen in the test. O-bite was used to record the mandibular position when speaking these letters. A full-adjusted articulator was used to find the mandibular position during speech, and the mandibular position was measured using a vernier caliper. The mandibular position during speech with intercuspal position was compared in both anterior-posterior and left-right directions of the horizontal plane. Multi-factor analysis of variance was conducted for the statistical analysis of the effect of objects and letters on the mandibular position. RESULTS: 1) The mandibular position was in front of the intercuspal occlusion position when speaking all seven letters, and almost no deviation was observed in the left and right directions (the mandibular position value of 82% was in the range of 0.5 mm). 2) Different objects had different mandibular positions during speech, whereas different letters did not. The distance between the centric relation position and the intercuspal position had a positive correlation with the range of the mandibular position during speech. CONCLUSION: The mandibular position was in front of the intercuspal position when speaking all seven words in the test. In the same object, the mandibular position was stable during speech.

Enhanced Biological Behavior of In Vitro Human Gingival Fibroblasts on Cold Plasma-Treated Zirconia.

OBJECTIVE: To evaluate whether atmospheric-pressure dielectric-barrier-discharge plasma treatment of zirconia enhances its biocompatibility with human gingival fibroblasts. MATERIALS AND METHODS: The zirconia disks were divided into four groups and treated using helium atmospheric-pressure dielectric-barrier-discharge plasmas for 30, 60 or 90 s or left untreated. The surface morphology, wettability and chemical elements were analyzed. Fibroblasts density, morphology, morphometry and attachment-related genes expression were measured at different time points from 3 to 72 h. RESULTS: After plasma treatment, the surface morphology and roughness remained the same, while the contact angle decreased from 78.31° to 43.71°, and the surface C/O ratio decreased from 3.17 to 0.89. The surficial areas and perimeters of HGFs were increased two-fold in the treated groups at 3 h. Fibroblasts density increased on treated disks at all time points, especially the ones treated for 60 s. Attachment-related genes in the groups treated for 30 and 60 s were significantly higher at 3 and 24 h. CONCLUSION: The helium atmospheric-pressure dielectric-barrier-discharge plasma treatment enhances the biological behavior of fibroblasts on zirconia by increasing the expression of attachment-related genes within 24 h and promoting the cell density during longer culture times. Wettability of zirconia, an important physicochemical property, has a vital influence on the cell behaviors.

[Ultrastructural study of sclerotic dentin in non-carious cervical lesions disposed by a total-etching dentin adhesive].

OBJECTIVE: To examine the ultrastructure of resin-infiltrated sclerotic dentine following the application of a three-step total-etching dentin adhesive. METHODS: Naturally-occurring, non-carious cervical lesions on extracted premolars were bonded using a total-etching dentin adhesive-Scotchbond Multi-purpose. Artificially prepared wedge-shaped lesions were also made in sound premolars and restored using the same adhesive as control. The morphological change of the dentin surface conditioned with the etchant, and the hybrid zone and resin tags in the dentin-resin interface were studied by SEM. RESULTS: Most dentinal tubules were obliterated by rod-like sclerotic casts in the non-carious cervical lesion, and could not be dissolved by Scotchbond Multi-purpose etchant. Both the hybrid zone and resin tags were observed in sclerotic dentin after restoration, although the resin tags were fewer and in lack of communications, the length of resin tags and the thickness of the hybrid zone were almost similar to those of the sound dentin. CONCLUSION: Bonding to sclerotic dentin is different from sound dentin, and may be compromised by the fewer resin tags and communications.

[Coverage errors of five shade guide systems to vital natural teeth].

OBJECTIVE: To compare the coverage errors (CE) of five different shade guides in anterio vital natural teeth of selected people. METHODS: Anterior vital natural teeth were measured with Crystaleye spectrophotometer, color coordinates of the teeth and five shade guides A (VITA Classical), B (VITA 3D-Master), C (Chromascop), D (Shofu Vintage Halo NCC) and E (Noritake)were analyzed with the supporting software. The CE of the five shade guide systems to natural teeth were evaluated in cervical, body and incisal regions, and difference in CE among shade guides was determined. RESULTS: In the cervical region, shade guide A had the maximal CE value (3.09 ± 0.97) and shade guide D had the minimal CE value (1.62 ± 0.75).In the body region, CE of shade guide B (1.65 ± 0.64) and shade guide D (1.52 ± 0.74) were lower than those of shade guides A (2.04 ± 0.80), C (2.04 ± 0.90) and E (2.02 ± 0.84) (P < 0.05).In the incisal part, all CE were below 2.00, and again shade guide A had the maximal CE value (1.81 ± 0.86) and shade guide D had the minimal CE value (1.28 ± 0.55). CONCLUSIONS: Within the limitation of the study, shade guide D had better color coverage of natural teeth in cervical, body and incisal regions.

An internet evaluation of Chinese public preferences for asymmetrically altered incisor angulations.

OBJECTIVE: To evaluate the Chinese public preferences for asymmetrically altered incisor angulations, with the goal of linking preferences to gender. METHODS: Five variations of 5 separate digital smiling photographs were used in this survey. The alterations included discrepancy between the dental and facial midlines, inclination of dental midline and two central incisors, inclination of left central incisor (mesially or distally) and occlusal cant. The raters used a 100-point visual analogue scale to evaluate each image on a web page. RESULTS: Overall 1,022 raters joined the evaluation and they were reliable (intraclass correlation coefficient = 0.76-0.80). Raters identified range of approval for several smile characteristics. A 2 mm dental to facial midlines discrepancy was the maximum acceptable deviation for females and 3 mm was the maximum for males. Females could accept a 4-degree occlusal cant and males could accept a 6-degree cant. These two characteristics were related to gender. The dental midline and relevant two central incisors with a 5-degree slope or less were generally acceptable. The approval of a left central incisor inclination was 5 degrees mesially and 10 degrees distally. These three characteristics were unrelated to gender. CONCLUSION: The approval for five smile characteristics could be identified reliably. The ranges of acceptability were large and slight changes in the angulations of incisors did not influence the smile attractiveness.

Reliability and accuracy of Crystaleye spectrophotometric system.

OBJECTIVE: to develop an in vitro shade-measuring model to evaluate the reliability and accuracy of the Crystaleye spectrophotometric system, a newly developed spectrophotometer. METHODS: four shade guides, VITA Classical, VITA 3D-Master, Chromascop and Vintage Halo NCC, were measured with the Crystaleye spectrophotometer in a standardised model, ten times for 107 shade tabs. The shade-matching results and the CIE L*a*b* values of the cervical, body and incisal regions for each measurement were automatically analysed using the supporting software. Reliability and accuracy were calculated for each shade tab both in percentage and in colour difference (ΔE). Difference was analysed by one-way ANOVA in the cervical, body and incisal regions. RESULTS: range of reliability was 88.81% to 98.97% and 0.13 to 0.24 ΔE units, and that of accuracy was 44.05% to 91.25% and 1.03 to 1.89 ΔE units. Significant differences in reliability and accuracy were found between the body region and the cervical and incisal regions. Comparisons made among regions and shade guides revealed that evaluation in ΔE was prone to disclose the differences. CONCLUSION: measurements with the Crystaleye spectrophotometer had similar, high reliability in different shade guides and regions, indicating predictable repeated measurements. Accuracy in the body region was high and less variable compared with the cervical and incisal regions.

[Ultrastructural study of sclerotic dentin surface following the application of the Er, Cr: YSGG laser].

OBJECTIVE: To investigate the ultrastructure character of sclerotic dentin surface conditioned by the Er, Cr: YSGG laser and acid etching. METHODS: Sixteen human teeth with sclerotic dentin were randomly assigned to 4 groups, and conditioned with acid etching (Group A), laser irradiation (Group B), laser irradiation after acid etching (Group C), or acid etching after laser irradiation (Group D) respectively. The characters of surface ultrastructure were observed using scanning electron microscope (SEM). RESULTS: In Group A, the majority of dentin tubules were blocked by sclerotic rods. In Group B, the honeycomb-like change was found on the sclerotic dentin surface. The surface structure of Group C was similar to that of Group B. In group D etching wiped off the honeycomb-like structure. CONCLUSIONS: The sclerotic dentin surface treated with laser irradiation turns into uniform honeycomb-like structure. The rough surface may be beneficial to bonding strength on sclerotic dentin after laser irradiation.