Influence of Manual and Ultrasonic Scaling on Surface Roughness of Four Different Base Materials Used to Elevate Proximal Dentin–Cementum Gingival Margins: An In Vitro Study
To evaluate and compare the effects of both manual and ultrasonic scaling on surface roughness of four different base materials, used for elevating dentin/cementum gingival margins of proximal cavities. Eighty human upper molars with compound Class II mesial cavities, with gingival margins 1 mm below the cemento–enamel junction (CEJ), were divided into four different groups according to the type of the base material used; resin-modified glass ionomer (RMGI), glass hybrid (HV-GIC), flowable bulk-fill resin composite (Bulk Flow) and bioactive ionic resin (Activa). This was followed by completing the restorations with the same resin composite. All materials were used according to the manufacturers’ instructions. All groups were further subdivided into two subgroups according to the scaling technique: manual (hand) or ultrasonic. All restorative and scaling procedures were performed after fixation of specimens with acrylic beside neighboring teeth to simulate natural contact. The mean surface roughness (Ra, μm) of all specimens was measured quantitatively and qualitatively by a three-dimensional (3D) surface analyzer system at two stages; (1) after thermal cycling for 5000 cycles without scaling and (2) after scaling. Data were statistically analyzed using analysis of variance (ANOVA), Tukey post hoc tests, and paired sample t-tests (at α=0.05). For baseline readings, the Bulk Flow group had the lowest Ra values, while HV-GIC group had the highest. RMGI and Activa groups had no statistical significant difference between their Ra values (p>0.05). For post scaling readings, hand scaling had significantly lower Ra values than ultrasonic scaling in all the material groups (p<0.05), except in the Bulk Flow group, where both scaling methods were not significantly different from each other (p>0.05) Bulk Flow had the smoothest surfaces when cured against a matrix band compared with the other tested base materials. When hand and ultrasonic scaling methods were compared, the latter technique had more detrimental effect on the surface texture of the four tested base materials.SUMMARY
Aim
Methods and Materials
Results
Conclusion
INTRODUCTION
Large posterior defects with proximal caries extending below the cemento–enamel junction (CEJ) and cavity margins located beneath the gingival tissues represent a very common clinical situation.1 Beside the challenges encountered during restoration of such defects, deep cervical margins are critical areas that may cause gingival irritation and periodontal pockets,1,2 especially if restorations are overhung or rough.3
The only structure that has a biological reaction after the invasion of the biological width is the connective tissue attachment, which is very selective about surfaces to be attached to; it needs cementum on one side and bone on the other. By contrast, epithelial attachment is not specific; it is capable of attaching to enamel, cementum, and restorative material, as long as the surface is hard, smooth, and clean.4In vivo studies showed a positive correlation between the surface roughness and the rate of supra and subgingival plaque accumulation that may lead to periodontal inflammation and an increased pathogenic bacterial colonization.5,6 These previous findings highlighted the importance of smooth restorations placed below the gingiva.
The health of periodontal tissue should be maintained using the least invasive approaches.7 Noninvasive periodontal treatment procedures, including scaling and root planning, are considered as the first line for management of the periodontal conditions.8 Different methods of scaling and root planning can control the gingival inflammation and bleeding index.9 In addition, a previous systematic review showed that subgingival mechanical debridement increased the mean attachment gain of gingival tissues.10 These noninvasive periodontal procedures are of a particular importance in subgingival Class II and V cavities.11 On the other hand, it was reported that all scaling methods have a negative effect on the surface smoothness of both the root and restorative materials.12–14 Thus, although periodontal benefits are obtained after scaling procedures, there is still the risk of increasing the surface roughness after these procedures, affecting the long-term success of the treatment.15
Proximal cavities with cervical margins below the gingiva are usually restored using either an open-sandwich technique or cervical margin relocation concepts,16,17 where direct restorations are used as a base for elevating the proximal cavity margin from an intracrevicular to a supragingival position and then completing the rest of the cavity with either direct or indirect options.17 Different base restorative materials were investigated in the literature for gingival margin elevation in such situations, including different modifications of glass ionomers and resin composites.18,19
Deep proximal cervical restorative surfaces are inadvertently subjected to different scaling procedures. Thus, the influence of such procedures on surface roughness of these restorative surfaces should be of interest. There is ample data regarding the effect of different scaling techniques on soft tissues, root surfaces, and even on restorative materials placed in Class V cavities. However, there are insufficient studies reporting the effect of scaling techniques on deep proximal cervical restorative surfaces. Therefore, this study evaluated and compared the effect of both manual and ultrasonic scaling on surface roughness of four different base materials, three of them were glass ionomer-based and one was resin composite-based, used for elevating dentin–cementum gingival margins of the proximal cavities. The research hypotheses were: (1) there is no difference in surface roughness between different base materials; (2) there is no effect on roughness of the four base materials following either manual or ultrasonic scaling.
METHODS AND MATERIALS
Materials
Four commercially available restorative materials were tested in the current study. Resin-modified glass ionomer (Fuji II LC) (RMGI), glass hybrid (EQUIA Forte) (HV-GIC), flowable bulk-fill resin composite (Tetric N-Flow Bulk Fill) (Bulk flow), and bioactive ionic resin (ACTIVA BioACTIVE RESTORATIVE) (Activa). The detailed description of the materials is presented in Table 1.
Cavity Preparation
Eighty sound human upper molars recently extracted due to periodontal disease were included in this study; they had approximately similar dimensions, and were examined with stereomicroscopy to confirm that they were caries and crack free, then cleaned of soft tissue and calculus deposits with ultrasonic scaler, and stored in 0.1% thymol solution until used.
Compound Class II cavities with standardized dimensions were prepared on the mesial surfaces of all teeth using cylindrical, medium-grit diamond burs (K881 012, öko DENT, Germany) under copious water coolant with a high speed handpiece (W&H, RC-90RM, Austria). A pencil was used to mark the outline before preparation. The cavity dimensions were: occlusal: 3 mm buccolingual width, 3 mm depth; box: 1 mm below the CEJ, 1.5 mm mesiodistal dimension at the cervical floor, and 4 mm bucco-lingual width.20 The margins were not beveled with slightly rounded line angels. A new bur was used after every five preparations. The dimensions were verified using a graduated periodontal probe.20 After preparation, cavities were examined for any defects. Buccal and palatal walls of the proximal boxes of all teeth were marked with pencil 1.5 mm above the CEJ (to mark the level of the base material) (Figure 1A,B).
Citation: Operative Dentistry 47, 2; 10.2341/20-007-C
Tooth Fixation
Following cavity preparation, each tooth was fixed with mesial and distal acrylic neighboring teeth (Banna, Alexandria, Egypt) using condensation silicone impression material (Silaxil putty, Lascod, Italy). The teeth were fixed in a way to simulate natural contact and correct occluso-gingival level of the three teeth.
The impression material was shaped using a dental wax carver (Lecron wax carver, Accurate Manufacturing, Pakistan) to simulate the correct contour and level of the gingiva around the teeth, especially parts simulating buccal and palatal gingival papilla. The impression material was kept at the level of buccal and palatal CEJ of the three teeth, then was left to set for 5 minutes before trimming of the excess using number #11 surgical blades (Tianda Medical Instruments Co, Huaian, China) (Figure 1C,D,E). Teeth were randomly assigned into four different groups, 20 molars each, according to the base material used. Each group’s teeth were numbered from 1 to 20, with a specific color for each material group on the distal surface.
Restorative Procedures
After preparation and fixation procedures, cavities were washed with water and dried. For RMGI and HVGIC groups, the gingival margins of the cavities were conditioned as recommended by the manufacturer with dentin conditioner (GC Co, Tokyo, Japan) for 20 seconds, followed by rinsing and drying. Occlusal and proximal enamel margins of all the cavities were selectively etched with 37% phosphoric acid (N-Etch, Ivoclar Vivadent, NY, USA) for 15 seconds, rinsed with water for the same time, excess water was blotted without desiccation. For Bulk Flow and Activa groups, a universal adhesive (Tetric N-Bond Universal, Ivoclar Vivadent, NY, USA) was applied before base placement on all cavity surfaces, air dried and light cured as recommended by the manufacturers’ instructions with a LED curing light (Elipar Deep Cure, 3M Oral Care, St Paul, MN, USA) operating at 1000 mW/cm2, and checked periodically after every 5 samples with a radiometer (Radiometer 100, Demetron Research Corp, Danbury, CT, USA).
Large-sized saddle contoured metal matrix bands with an enlarged subgingival ledge (N 1.313-0.035 mm, Tor VM, Moscow, Russia) with Small Spring clip (N 1.003 Tor VM, Moscow, Russia) were applied around each cavity while making sure that the end of the band was beyond the gingival margin of the cavity. Then, a suitable-sized plastic wedge (Diamond Wedges, Bioclear, Tacoma, WA, USA) was applied in the gingival embrasure between each tooth and neighboring premolar, ensuring intimate adaptation between the gingival margin of the cavity and internal surface of the band (Figure 1F,G). After that, each group was restored up to 1.5 mm above the CEJ using the group specific base material in a bulk technique (Figure 1H,I). All base materials were mixed, dispensed, and cured (RMGI, Activa and Bulk Flow groups) according to the manufacturers’ instructions. For RMGI and HV-GIC groups, the universal adhesive was applied after base placement with the same technique mentioned earlier. The remaining cavity was restored with a nanohybrid resin composite material (Tetric N-Ceram, Ivoclar Vivadent) that was inserted in the cavity in 2-mm horizontal increments using a plastic instrument until the cavity was completely filled.21 Each increment was cured from the occlusal surface for 20 seconds. Additional curing for 40 seconds was performed from the proximal surface after removal of the wedge and matrix band (Figure 1J).
All specimens were stored in distilled water at 37°C for 24 hours in an incubator (BTC, Model: BT1020, Egypt) prior to the finishing and polishing procedures.22 Finishing and polishing of the occlusal surfaces was performed with Al2O3 discs (Tor VM, Moscow, Russia) using a low-speed handpiece (Strong 204, Daegu, South Korea) under water cooling; proximal surfaces were kept without finishing and polishing to simulate clinical situations (Figure 1K,L). All procedures were performed by a single operator using magnification (4×loupes, Amtech, Wenzhou, China).
Thermocycling
After restoration, each specimen was removed from the rubber base block. All specimens (n=80) were thermocycled for a total number of 5000 cycles (SD Mechatronik thermocycler, Germany), which represents approximately 6 months of clinical service before scaling.23 The specimens were alternated between 5°C and 55°C ± 2°C, according to ISO 11405 (International Standards Organization) recommendations, continuously checking for water temperature, with a dwell time of 15 seconds and a transfer time of 5 seconds.24 Afterwards, all the specimens were carefully evaluated under an optical microscope to check for cracks. Finally, each specimen was fixed in a second rubber base block where the mesial surface to be evaluated was facing upwards to facilitate roughness evaluation (Figure 1M).
Pre-instrumentation Roughness Reading
The area of the base material (2.5 mm × 4 mm) was marked with pencil, and then divided into buccal and palatal haves. Each half was assessed quantitatively and qualitatively for surface roughness using a 3D surface analyzer system. Each half was photographed using a USB digital microscope with a built-in camera (U500× Capture Digital Microscope, Guangdong, China) connected with an IBM compatible personal computer using a fixed magnification of 120× and a resolution of 1280×1024 pixels per image. The digital microscope images were cropped to 350×400 pixels using Microsoft Office picture manager to specify and standardize the area of roughness measurement. The cropped images were analyzed using WSxM software (Ver 5 develop 4.1, Nanotec, Electronica, SL, Spain) where a 3D image of the surface profile was created.25,26 Three 3D images with an area of 10 μm × 10 μm were collected at different sites for each half; then the average of the three readings were recorded as the surface roughness (Ra, μm) value for either buccal side or palatal side to serve as the prescaling baseline controls.12
Scaling
After initial roughness evaluation, each group was further subdivided into 2 subgroups (n=10) according to the scaling technique; (1) hand scaling subgroup, or (2) ultrasonic scaling subgroup, and returned back to the rubber base mold with the same proximal and occlusal relation with the two neighboring teeth used for restoration.
For hand scaling subgroups, a Gracey curette (no 11/12; Goldman Products Inc, Wauconda, IL, USA) was used. Each buccal/palatal side received 10 apical to coronal consecutive strokes parallel to the long axis of the tooth using medium force,12,27 each side of the curette was used with either buccal or lingual side scaling, and when the interproximal side was changed, the side of the curette was replaced. Curettes were sharpened using a ceramic sharpening stone (SST-C3, Osung, Seoul, South Korea) after every tooth. A sharp, new curette was used for each group (Figure 1N).
For ultrasonic scaling subgroups, a piezoelectric ultrasonic scaling device (Intelligence PS-25, Rolence Enterprise Inc., Taoyuan, Taiwan) with one type of subgingival fine-diameter ultrasonic tip was used (P1, Woodpecker, Guangxi, China).28 The machine was operated according to the manufacturer’s instructions under profuse water irrigation for cooling of the scaler tip at medium power settings, standard lateral force, and a frequency of 29 kHz for all specimens.13,14 The side of the scaler tips were placed in the mesial interproximal areas from both buccal and palatal sides (between each specimen and premolar) 1-mm below the gingival simulation with zero angulation in relation to the base material.11,29 Each side received 10 apical to coronal consecutive strokes.29 A new scaler tip was used for each group (Figure 1O).
One experienced periodontist instrumented all the specimens who was blind to the restoration step. Following instrumentation, all the specimens were removed from the rubber base mold, thoroughly rinsed with water for 10 seconds, and then cleaned in an ultrasonic cleaner for 3 minutes. Finally, specimens were placed back in the second rubber base block for roughness evaluation.
Postinstrumentation Roughness Evaluations
The same areas of base materials were evaluated for the second time, as previously described in the preinstrumentation roughness evaluation.
Statistical Analysis
Sample Size Calculation—The sample size for this study was calculated before conducting any work using G*Power program (G*Power Ver. 3.0.10, Kiel, Germany).13 The total sample size of 64 teeth achieved 80% power (equal to type II error); type I error (α) was 0.05. Due to the new methodology proposed by our study, two more teeth were included in each subgroup to have a total sample size of 80 teeth.
Statistical Methods—The Ra values for buccal and palatal sides for both control and scaling subgroups of all base material groups were compared using independent sample t-tests; when there was no significant difference, the Ra value of each tooth with each scaling technique tested was calculated by obtaining the mean Ra value of the six readings combined, three from the buccal side and three from the palatal. All data were statistically analyzed using SPSS (SPSS version 20, IBM, Chicago, IL, USA). Ra values proved to be normally distributed after they were subjected to the Shapiro–Wilk test, and the homogeneity of variances was tested using Levene’s test; so parametric tests were used to compare the study groups. One-way analysis of variance (ANOVA) was used to compare the control groups of the four materials; when significant differences were detected, a pairwise comparison was performed using Tukey post hoc tests (at α=0.05). The effect of scaling technique per each material group was evaluated using paired sample t-tests. Two-way ANOVA was used to determine the effect of study variables (base material type and scaling technique), and their interaction on surface roughness followed by Tukey post hoc test (at α=0.05).
RESULTS
One-way ANOVA revealed that baseline Ra readings for all the groups were statistically significant (p<0.05). The mean Ra values and standard deviations for baseline readings are presented in Table 2. Pairwise comparisons revealed that Bulk Flow had the lowest Ra values followed by RMGI and Activa, respectively; the latter two had no statistically significant difference between their Ra values. The highest Ra values were shown by HV-GIC.
Paired sample t-test results (Table 3) revealed that, regardless of the base material used, both scaling methods adversely affected the surface smoothness in a significant way (p<0.05).
Two-way ANOVA showed that both study variables significantly affected the Ra values (p<0.05); the interaction between them were also significant (p<0.05). The mean Ra values and standard deviations for subgroups of all the base materials are presented in Table 4. Tukey honestly significant difference (HSD) multiple comparisons revealed that manual scaling had significantly lower Ra values than ultrasonic scaling in all groups (p<0.05), except in the bulk flow group, where the scaling methods were not significantly different (p>0.05). RMGI, Bulk Flow, and Activa hand scaling subgroups had the lowest Ra values; on the other hand, HV-GIC ultrasonic subgroup had the roughest surfaces. Representative 3D and histogram images for the four base materials are shown in Figure 2.
Citation: Operative Dentistry 47, 2; 10.2341/20-007-C
DISCUSSION
Previous clinical and histological studies have linked the presence of subgingival cervical margins and the increase in bacterial plaque, gingival indices, and probing depth.1,11 Smooth subgingival restorations are required to prevent jeopardizing the periodontal health in these critical areas.30 Therefore, this study evaluated and compared the surface roughness of different restorative materials placed below the CEJ in clinically simulated subgingival restorations, in order to determine the smoothest base material to be used in restoring such defects.
The main objective of prevention and/or treatment of periodontitis includes periodic removal of plaque and calcified deposits from the teeth and restorations.8 This procedure is usually accomplished by different scaling techniques that may accidently not only affect the dental tissues but also the restorative surfaces creating roughness that may lead to unfavorable periodontal consequences.11 Thus, this study also evaluated the effect of scaling techniques on roughness of restorations placed below the CEJ, to determine the most suitable scaling technique in proximal subgingival restored areas.
The selection of the four tested base materials was based on both open-sandwich technique and cervical margin relocation concepts.16,17 The open-sandwich technique includes using conventional glass ionomer cement (GIC) for elevation of the gingival margin. High clinical failure rates have been reported with this material.31 Thus, modifications using RMGI and HV-GIC have been introduced to be used with this technique with acceptable long-term outcomes.18,32 Recent studies argue that glass ionomer with its hydrophilic nature, flexibility, and chemical bonding could be a more suitable option for bonding to deep, moist dentin–cementum margins.33,34 That is why RMGI and HV-GIC were included in this study as base materials.
On the other hand, cervical margin relocation includes using a flowable resin composite base to lift the proximal gingival margin. Kielbassa and others31 reported how promising this technique is in their systematic review. Bulk-fill resin composites have been developed with different chemical compositions to reduce polymerization shrinkage stress. In addition, they can be placed in layers up to 4 mm in thickness and cured in one single step.19 Thus, they can be quickly applied and save chair time, especially when used for deep and large cavities.35 Previous studies found higher bond strength for flowable bulk fill compared to nanofilled layered composites when bonded to proximal dentin–cementum margins;20,36 moreover, others reported promising marginal adaptation of flowable bulk fill with such margins.37 That is why a flowable bulk-fill material was tested in this study.
Bioactive restorative materials are a relatively new category that react to pH changes in the mouth by providing calcium, phosphate, and fluoride ions to maintain the chemical integrity of the tooth structure. ACTIVA BioACTIVE restorative is one in this category.38 Benetti and others39 stated that this material has a promising mechanical behavior, as it showed comparable flexural strength and fracture toughness to flowable and bulk-fill resin composites.40,41 On the other hand, the material’s compromised hardness suggests the importance of using an abrasive-resistant resin composite as coverage.42 That is why it was used in this study as a base material.
This study included two different scaling methods: hand and ultrasonic. Scaling and root planning by curettes (hand) are the most frequently used procedures for removing of subgingival calculus and treatment of periodontal diseases, due to their low cost and effectiveness in reducing the clinical signs of inflammation and the levels of pathogens.43 Despite different developments in scaling techniques, hand instrumentation is still considered the gold standard.44 Ultrasonic scaling is considered to be less strenuous for the operator and more comfortable for patients than hand scaling, and can be performed in considerably less time.44 Thus, it has become increasingly popular for subgingival debridement.28
Upper molars were used in this study, as their buccal surface is the second most predominant site for supragingival calculus deposition after the lingual surface of the six lower anterior teeth.45 Supragingival calculus creates an environment more conducive to subgingival plaque accumulation,46 thus, a significant association between supra- and subgingival calculus was found,46 indicating the importance of subgingival scaling and root planning in upper molars area.
After cavity preparation, the teeth were fixed with neighboring teeth using condensation silicone impression material (putty consistency). This material was selected based on several fixation trials with other materials like wax, stone, and impression compound. These trials failed due to both distortion and brittleness that prevented good fixation of teeth or due to excess stiffness that prevented placement of matrix bands and wedges for restoration.
Contoured sectional bands and wedges were used during restoration to create correct clinically simulated contact areas, gingival embrasures, and proximal surface contour.47 The cavities were filled with base materials up to 1.5 mm above the CEJ that nearly corresponded to the level just below the proximal contact, which was then built with overlying resin composite with the rest of the cavity. Interproximal wear usually affects the proximal contact tightness, and consequently the contact should be built with hard and strong restorative materials,48 like the overlying resin composite used in this study. Five thousand cycles of thermocycling was performed to simulate 6-months of clinical service before scaling procedures.23 This was chosen based on the frequent 6-month scaling and prophylactic polishing interval performed by most of the dentists.49
In this study, evaluation of surface roughness was performed both quantitatively and qualitatively in a nondestructive method, to allow detailed visualization for the surface without contact.50 This would accurately allow further recording of roughness values for the same specimens after scaling.
All scaling procedures were carried out by one periodontist to eliminate interoperator variability and minimize variations in stroke length, force, and pressure applied during instrumentation. A piezoelectric ultrasonic unit was chosen in this study, as its oscillation pattern produces movement that is primarily linear in direction, in contrast to magnetostrictive devices with their circular motion.28 This linear motion provides more efficient calculus removal with less damage to the surface being scaled.51 A number of in vitro studies demonstrated that working parameters such as power settings and tip angulation can determine the amount of damage for the root or restoration surface.28,51 The device was operated at medium power settings as a previous review mentioned that increasing the power settings from medium to high can lead to high surface roughness and alterations.52 Narrow probe-shaped tips were used in this study, as it was reported that they are less aggressive to root dentin than wide probe-shaped tips.28 In piezoelectric units, tip angulation has the most important effect on surface alteration depth of the scaled surfaces.52 The least surface damage was obtained when the tip was used at zero angulation,52 as was used in the current study.
Although there was no significant difference between Ra values for buccal and palatal sides for either control or subgroups of all material groups, it is worth mentioning that roughness values from the palatal side were higher than the buccal side in most of the specimens. This could be explained by the wider gingival embrasure on the palatal side than buccal embrasure,53 making either curette or ultrasonic tip touch a wider surface palatally, thus creating more roughness.
The results of this study showed that Ra baseline readings differed among the four base materials; Bulk Flow had the smoothest surfaces, while HV-GIC had the roughest, therefore, the first null hypothesis was rejected. The literature has already shown that curing of resin-based materials against a matrix band can produce a relatively smooth surface compared with any finishing and polishing procedures.54,55 This smooth surface is related to the resin-rich layer that is accumulated against the band.55 A previous study explained that the compression applied through the matrix band on the surface of the resin-based materials can probably cause the filler particles to slide in the organic matrix, so that smaller particles, with lower density, appeared more and closer to the top in relation to the larger ones.56 This may indicate that filler particle shape and size can have a minor role in affecting the surface roughness when curing the resin-based materials against the matrix band. HV-GIC has no resin methacrylate content; its composition is mainly formed of 90%–95% strontium fluoroalumino silicate glass (FAS) (25 μm),57 which mostly protruded on the surface when the material was left to set against the matrix band, thus having the highest roughness values among the base materials. The amount of resin in the RMGI used in this study was 1%–5% [2-hydroxyethyl methacrylate (HEMA)], most of its composition also contains FAS;57 this heterogeneous and biphasic chemical composition can explain why it has higher roughness values than Bulk Flow.
Activa contains 42 wt% organic resin, while Bulk Flow contains 28 wt%. The organic resin of Activa is called an “ionic resin,” which has a more hydrophilic nature compared to Bulk Flow and contains a small amount of water. This aqueous ionic resin may cause the material to be more susceptible to matrix degradation after thermal cycling, as was previously reported.58 Yilmaz and others59 showed that following thermal cycling, the hydrophilicity of the material allowed water to penetrate more easily, leading to matrix degradation, exposing the underlying filler particles and increasing its roughness.
The results of the current study showed that regardless of the scaling technique used, the roughness values increased significantly compared with baseline readings, which means the second null hypothesis was rejected. This is in accordance with previous studies that examined the scaled surfaces under scanning electron microscope (SEM) and found valleys, cracking at the filler–matrix interface, filler dislodgment, and even removal of a whole layer of the root surface or restoration,11,29,60 and reported that this surface alteration is an unavoidable complication of the scaling procedures.
The hand scaling technique had smoother surfaces than the ultrasonic technique for all the base materials in this study, except for Bulk Flow where both the scaling methods created comparable roughness values. This could be explained by the finding of a previous study showing that hand scaling instruments usually made greater contact area with the surface than ultrasonic tips;29 a greater contact area could result in masking the roughness created by the instrument resulting in smooth surface. Mishra and others61 noticed that hand scaling resulted in more surface flattening than ultrasonic scaling, and attributed the smooth surface they found after hand scaling to this surface loss. Moreover, hand scaling was reported to facilitate better tactile proprioception and controlled movement to the operator, resulting in a smoother surface.62 A possible explanation for the increased Ra values for ultrasonic subgroups is the vibration effect of the ultrasonic scaling that could potentially create more cracks and greater filler dislodgement.13 Conversely to the current results, previous studies found that ultrasonic scaling produced smoother surfaces when compared to hand scaling.63,64 The difference in results could be attributed to different experimental designs, including surfaces to be scaled, in the current study restorative materials and in the former studies root dentin, methods of roughness evaluation, in addition to different characteristics of the instruments like shape, size and material of the tips used, and different force and pressure of application due to operator variability.
Although the tested HV-GIC used in this study was reported to have promising wear resistance and microhardness results compared with other types of glass ionomers,65,66 its roughness values increased significantly after both scaling techniques, especially after ultrasonic scaling. During scaling procedures, the weak polysalt matrix phases in HV-GIC, which usually press against the matrix band, were easily removed while the harder unreacted FAS glass particles protruded from the surface;60 this may explain why this material had the highest Ra values among the other scaled base materials. In addition, Buldur and others65 observed deep cracks, pits, and fissures after aging on the same material surface under SEM, even if the surfaces were varnished; so maybe ultrasonic scaling increased these already existing cracks and resulted in the highest roughness values.
For resin-based materials, the resin-rich layer that forms the smooth surface resulting from adaptation of the material against the matrix band during restoration is usually removed after any surface alteration,67 like scaling procedures in this study. Consequently, inorganic fillers have an effect on surface roughness. The surface roughness values increased with the increase of the filler particle size.11,13,14 RMGI, Activa, and Bulk Flow have nearly the same filler particle size (5 μm); this may explain the comparable Ra results after hand scaling. On the other hand, after ultrasonic scaling, both RMGI and Activa Ra values differed significantly. This may be explained by the results of previous studies showing significantly higher wear resistance with Activa compared to the RMGI used in this study;66,68 the authors partially attributed the cause to the resilient resin matrix with energy-absorbing elastomeric components of Activa.68 This higher wear resistance may lead to less degradation by ultrasonic scaling and subsequent lower inorganic filler exposure and roughness values.11 Another possible reason was suggested by Garoushi and others,68 as they found that the RMGI used in this study had a greater initial burst of fluoride release than Activa. Leaching of ions from filler particles of regular fluoride-releasing materials was attributed previously to filler–matrix debonding, because of a weakened filler. This leads to microcracks and higher degradation of the material69; these cracks may be aggravated by ultrasonic scaling.
Bulk Flow was the only material that showed no significant difference between scaling methods. The smooth surfaces of this material could be related to filler shape. The Bulk Flow used in this study has homogenous, rounded-shaped fillers compared with the irregular, heterogeneous-shaped fillers in other base materials. Marghalani and others67 concluded that spherical-shaped fillers may allow more flow and stress relaxation of the material resulting in smooth surface compared to irregular ones that may develop stress concentration around them. Another possible reason is the form in which Bulk Flow is supplied. Bulk Flow is a single component material, whereas in the case of glass ionomers and Activa, powder has to be mixed with liquid or two pastes have to be mixed, respectively, therefore risking more air bubble incorporation and increased porosity.66 These porosities may get enhanced after ultrasonic instrumentation leading to greater surface roughness. The Bulk Flow used in this study is not like conventional flowable composite with their lower filler amount; instead, the filler content reaches 68.2 wt%, leading to high wear resistance and less susceptibility to degradation by ultrasonic devices.11
The literature suggests that the critical threshold of roughness for patients was nearly 0.3 μm, and the threshold for biofilm accumulation was 0.2 μm70; so it could be inferred that, in the current study, none of the materials’ roughness with either scaling technique would be perceptible by the patient, and that HVGIC with both scaling techniques and RMGI when ultrasonically scaled would be at a risk for biofilm accumulation. Considering that their Ra values were just above the biofilm threshold, it is worth mentioning that Quirynen and others71 found that variations around biofilm threshold had only a negligible impact on bacterial adhesion. In addition, a recent study showed that surface roughness had a minor role in the retention of a fully grown biofilm.72
It should be recognized that the present in vitro study has limitations; the scaling techniques were performed by one operator; consequently, the manual pressure exerted, even after specific training, cannot be considered replicable or standardized. In addition, only two scaling techniques were assessed among different other promising scaling methods. The methodology performed in the current study is new and intended to simulate the clinical situation, so further in vitro studies, including microbiological adhesion assessment and even histological evaluation for the attachment of gingival epithelial cells to the tested base materials’ surfaces, are needed. In addition, clinical studies are required to assess periodontal healing in critical dental areas, like below the proximal CEJ, after different scaling methods for debridement of microbial deposits on restorative materials placed in such areas.
CONCLUSIONS
Within the limitations of the present study, the following may be concluded:
In terms of surface roughness, the evaluated resin-based composite may be recommended to restore subgingival proximal margins rather than the tested glass ionomer-based restorative materials, especially when curing and setting of these base materials are done against a matrix band.
Both hand and ultrasonic scaling methods had a negative effect on the surface quality of the four tested base materials, so they should be performed with caution when used on restored subgingival proximal areas.
Considering changes in surface texture following the use of each scaling technique, the present study showed that hand scaling may be preferable to ultrasonic scaling for the tested base materials, especially for glass ionomer-based restorative materials.
Methodology steps for a representative specimen (Bulk Flow). A: Proximal cavity part outline and dimensions, the three lines mark 1.5 mm above CEJ, CEJ, 1 mm below CEJ. B: Occlusal cavity part outline and dimensions. C: Occlusal view for fixing the teeth in silicone impression material (putty consistency). D,E: Buccal and palatal views for fixation. F,G: Occlusal and buccal views for the Saddle matrix band and diamond wedge in place. H,I: Occlusal and buccal views after base placement, black arrow indicates the base material level (just below the contact). J,K: Occlusal views for the final restoration before and after finishing and polishing. L: Buccal view for the final restoration (black arrow indicates the level of base material/junction between base material and overlying composite). M: Specimen in the 2nd silicone block for roughness evaluation, the margins of the base material were marked and divided into two halves—buccal and palatal. N: Gracey curette (no. 11/12) in place. O: Ultrasonic tip was placed at zero angulation while the end of the tip 1 mm below gingival simulation.
Representative 3D and histogram images for the four base materials. For 3D images, spikes at the borders are artifacts. For histogram images, the Y axis represents the number of repetitions for each reading (μm), the Ra value was recorded as the mean of the five readings with the highest repetitions. A,B: Representative 3D and histogram images for hand scaling subgroup in RMGI group. C,D: Ultrasonic in HV-GIC. E,F: Control in Bulk Flow. G,H: Hand in Activa.
Contributor Notes
Clinical Relevance
In terms of surface roughness, resin-based composite could be recommended for gingival margin elevation of subgingival proximal cavities rather than glass ionomer-based restorative materials. Whenever noninvasive periodontal treatment is required for such restored cavities, hand scaling may be preferable rather than the ultrasonic method.