Eighteen-month clinical performance of preheated nanoceramic resin-based composites in Class I occlusal cavities: A randomized clinical trial.

Aims: This study aimed to evaluate the effect of preheated nanoceramic resin-based composite (RBC) (Ceram-X-Mono) placed in Class I occlusal cavities over a period of 18 months. Settings and Design: This study involves split-mouth design, randomized controlled clinical trial (RCT). Materials and
Methods: One operator restored 60 Class I occlusal cavities in 24 patients. Preheating of nanoceramic RBC to 60°C for 10 min was performed before insertion of the material into 30 prepared cavities, whereas 30 restorations in the nonpreheated group were placed according to the manufacturer's instructions. Two observers evaluated the restorations using Federation Dentaire Internationale (FDI) criteria at baseline, 6, 12, and 18 months. Statistical Analysis: Kappa index, Friedman and Wilcoxon matched pair test, and Krushal-Wallis and Mann-Whitney tests were used for statistical analysis.
Results: 100% retention rates were seen in both the groups. In nonpreheated group, significant difference was observed for surface staining (P = 0.0001), color stability (P = 0.0277), anatomic form (P = 0.0431), and marginal adaptation (P = 0.0051), whereas in preheated group, significant increase in surface staining (P = 0.0051) was recorded. There was a statistically significant difference observed between the preheated and nonpreheated groups at different time periods for the tested clinical parameters.
Conclusion: Within the limitations of this RCT of 18 months, preheated nanoceramic RBC restorations showed better clinical performance compared to nonpreheated group. Copyright:

INTRODUCTION

In today's era of dentistry, resin-based composite (RBC) material occupies a major part as a direct restorative material.[1] High esthetics, ability to bond to tooth structure, and minimally invasive cavity designs make RBC the material of choice.[2]

However, one of the inherent drawbacks of RBC is polymerization shrinkage which will clinically manifest as marginal breakdown, secondary caries, and postoperative sensitivity, inevitably leading to failure of restorations.[23] In addition, many of the contemporary RBC are difficult to handle and sticky resulting in air entrapment and voids formation while placement.[2]

To overcome these demerits, newer materials and methods such as incremental technique,[1] soft-start polymerization,[4] placing a liner, and prewarming[2] the RBC are recommended.

Ceram-X-Mono is one such material introduced through a combination of Ormocer and nanotechnology. This composite contains methacrylate-modified silicon dioxide containing nanofillers and resin matrix with highly dispersed methacrylate-modified polysiloxane particles. Manufacturer claims it has superior mechanical properties compared with RBC which makes it suitable for direct restorations.[5]

Preheating holds a promising method among the different techniques employed to reduce polymerization shrinkage. Choudhary et al. suggested preheating the RBC to 54°C increases the adaptation and lowers the total surface area.[2] Studies have reported that preheating enhances mechanical properties.[67]

Nevertheless, all the above studies were conducted in laboratory conditions which could not simulate the oral environment.[1267] Hence, the aim of the present study was to evaluate the clinical performance of preheating nanoceramic RBC (Ceram-X-Mono) placed in posterior Class I occlusal restorations over a period of 18 months.

MATERIALS AND METHODS

The clinical trial was carried out after gaining approval from the Institutional Ethical Committee (D189001029) and was registered under Clinical Trial Registry India (CTRI/2020/08/027474) which was conducted according to CONSORT guidelines [Figure 1].

Figure 1

Consort flow diagram

Twenty-four patients aged between 18 and 45 years were selected for the study. The sample size was calculated using PS Version 3.1.2. Written informed consent was obtained from each patient.

Inclusion criteria

Good oral hygiene, bilateral permanent molars or premolars with Class I lesions (International Caries Detection and Assessment System) ICDAS II Score 3 or 4,[8] with at least one neighboring tooth in occlusion to antagonistic teeth, and patients with no clinical history of allergies to dental products were included in the study. The teeth to be restored had to be vital and without pulpal or periodontal disease, pain, and preoperative sensitivity.

Exclusion criteria

Patients with fewer than 20 teeth, rampant caries, bruxism habits, periodontal problems, pathologic pulpal diagnosis with pain, fracture or visibly cracked teeth, defective restoration either adjacent or opposing to the tooth, atypical extrinsic staining of the teeth or staining of any tooth-colored restorations, pregnant and lactating women, and patients with serious health issues were excluded frrom the study.

Randomization

Simple randomization was done by generating numbers from 1:60 using a random sequence generator (Randomness and Integrity Services Ltd.). The generated random number was assigned with one of the restorative techniques on the right side of the patient's arches. Similarly, the left side of the mouth was assigned to receive the other designed restorative technique. Each patient received both the restorative techniques randomly in this split-mouth design. These data were kept concealed in numbered, opaque, and sealed envelopes which were opened directly before preparation of the cavity for each patient.

Restorative procedures

Bitewing and intraoral periapical radiographs of the teeth to be restored were taken preoperatively. A single experienced operator placed 60 restorations in total.

Patients were anesthetized and rubber dam isolation was performed. To evaluate the cavity depth, a Williams periodontal probe was used. The average faciolingual width of the prepared cavities was about one-third of the intercuspal width. Cavities were prepared with No. 245 tungsten carbide bur with uniform depth and floor in dentin.

After the cavity preparation, enamel was etched with 37% phosphoric acid for 15 s. Teeth were then thoroughly rinsed and blot dried. Universal adhesive (Single Bond Universal 3M ESPE, St. Paul, MN, USA) was applied and light cured for 10 s curing light in standard application mode at an output of 1000 m W/cm.[2] (Elipar3M ESPE, St. Paul, MN, USA).

Smart dentin replacement (SDR) flowable RBC (Dentsply Caulk, Milford, DE, USA) was applied in a first layer and was light cured for 20 s. Cavities were restored using Ceram-X-Mono (Dentsply De Trey Konstanz, Germany) and light cured to 20 s according to the manufacturer's instructions [Table 1].

Table 1

Materials used in the study

Brand name	Specification	Manufacturer and lot number	Composition
Ceram. X Mono Sphere TEC one	Ormocer-based/nanoceramic resin composite/nanohybrid	Dentsply DeTrey, Konstanz, Germany Lot no. #1808000572	Matrix – Methacrylate-modified polysiloxane (organically modified ceramic), dimethacrylate resin, fluorescent pigment, UV stabilizer, camphorquinone, ethyl-4(dimethylamino) benzoate, iron oxide pigments, titanium oxide pigments, aluminum sulfo silicate pigments
			Filler – Barium–aluminum–borosilicate glass, methacrylate functionalized silicon dioxide nanofiller
SureFil SDR Flow	Bulk-Fill flowable resin composite	Dentsply Caulk, Milford, DE, USA Lot no. #1809000238	Matrix: Polymerization modulator, dimethacrylate resins, UDMA
			Filler: Ba-B-F-Al silicate glass, SiO2, amorphous, Sr-Al silicate glass, TiO2
Single-bond Universal	Universal adhesive	3M ESPE, St Paul, MN, USA Lot no. #657055	MDP phosphate monomer, HEMA, copolymer of acrylic/itaconic acids, diurethane dimethacrylate, glycerol dimethacrylate, water and ethanol, silane

MDP: Methacryloyloxydecyl dihydrogen phosphate, UV: Ultraviolet, UDMA: Urethane dimethacrylate, HEMA: Hydroxyethyl methacrylate

In preheated group, nanoceramic RBC material was warmed to a temperature of 60° C in a customized composite preheater for 10 min. This preheated RBC was immediately carried into the cavity and light cured for 20 s.

After finishing the restorative procedures, the rubber dam was removed and occlusal adjustments were made using fine and ultrafine diamond burs (Mani, Inc., Japan). All restorations were finished using flame-shaped finishing stones and polishing points (Shofu, Inc., Japan).

Two experienced senior faculty in the department evaluated the restorations independently. Restorations were evaluated according to the FDI criteria[9] [Table 2] for baseline, 6, 12, and 18 months. All the restorations were evaluated under dental operating light using size no. 5 flat surface mouth mirrors and 23/17 dental explorers. Photographs and digital intraoral radiographs were taken at each follow-up visit.

Table 2

Federation dentaire internationale criteria

Score	Surface staining	Color stability	Anatomic form	Fractures and retention	Marginal adapatation	Postoperative sensitivity
Clinically very good	No surface staining	Good color match. No difference in shade and translucency	Form is ideal	Restoration retained, no fractures/cracks	Harmonious outline, no gaps, no discoloration	No hypersensitivity, normal vitality
Clinically good	Minor staining, easily removable	Minor deviations	Form is only affected	Small hairline crack	Marginal gap Small marginal fracture removable by polishing	Low hypersensitivity for a limited period of time, normal vitality
Clinically sufficient/satisfactory	Moderate surface staining, also present on other teeth, not esthetically unacceptable	Clear deviation but acceptable. Does not affect esthetics: More opaque More translucent Darker Brighter	Form differs but is not esthetically displeasing	Two or more or larger hairline cracks and/or chipping (not affecting the marginal integrity or proximal contact)	Gap<250 µm not removable Several small enamel or dentin fractures	Premature/slightly more intense Delayed/weak sensitivity; no subjective complaints, no treatment needed
Clinically unsatisfactory	Surface staining is present on the restoration and is unacceptable; major intervention necessary for improvement	(Localized) clinically unsatisfactory but can be corrected by repair Too opaque Too translucent Too dark Too bright	Form is affected and unacceptable esthetically. Intervention (correction) necessary	Chipping fractures which damage marginal quality or proximal contacts; bulk fractures with or without partial loss (less than half of the restoration)	Gap>250 µm or dentin/base exposed Chip fracture damaging margins Notable enamel or dentin wall fracture	Premature/very intense Extremely delayed/weak with subjective complaints Negative sensitivity. Intervention necessary but no replacement
Clinically poor	Severe staining and/or subsurface staining (gene-ralized or localized); not accessible for intervention)	Unacceptable. replacement necessary	Form is completely unsatisfactory and/or lost. Repair not feasible/reasonable, replacement needed	(Partial or complete loss) of restoration	Filling is loose but in situ	Very intense, acute pulpitis or nonvital. Endodontic treatment is necessary and restoration has to be replaced

The data obtained were statistically analyzed using SPSS 20.0 version (SPSS Inc., Chicago, IL, USA). To determine the degree of agreement between the two evaluators, kappa index was used. All the clinical parameters at baseline, 6, 12, and 18 months were analyzed using Krushal-Wallis test. Comparison between the preheated and nonpreheated group was performed using Mann-Whitney U-test. Friedman and Wilcoxon matched-pair test was used to analyze the clinical parameters at different time intervals for each individual group. P < 0.05 was taken as a level of significant difference.

RESULTS

Out of 23 patients, 13 were female and 10 were male. A total of 60 restorations were distributed among 23 maxillary molars and 37 mandibular molars. The recall rate was 100% at 6 months and 83.3% at 12 and 18 months. In the present study, inter-examiner agreement was observed to be 95%–98% at different time periods.

Table 3 shows the summary of clinical data at recall visits for the parameters observed in the study. All the 60 restorations in both the groups were retained throughout the recall period.

Table 3

Summary of results

Criteria	Score	Nonpreheated control group				Preheated experimental group
		Baseline	6 months	12 months	18 months	Baseline	6 months	12 months	18 months
Surface staining	1	30/30	20/30	14/26	12/26	30/30	26/30	22/26	22/26
	2		10/30	12/26	14/26		4/30	4/26	4/26
Color match/stability	1	30/30	30/30	24/26	23/26	30/30	30/30	26/26	26/26
	2			2/26	3/26
Anatomic form	1	30/30	27/30	23/26	23/26	30/30	30/30	26/26	26/26
	2		3/30	3/26	3/26
Fracture/retention	1	30/30	30/30	26/26	26/26	30/30	30/30	26/26	26/26
Marginal adaptation	1	30/30	26/30	22/26	22/26	30/30	30/30	26/26	26/26
	2		4/30	4/26	4/26
Postoperative sensitivity	1	29/30	29/30	26/26	26/26	30/30	30/30	26/26	26/26
	2	1/30	1/30

Tables 4a and b show a significant rise in the scores from 1 to 2 for surface staining, marginal adaptation, color stability, anatomic form, postoperative sensitivity in nonpreheated group, whereas in preheated group, there was a significant rise in FDI scores for surface staining with P < 0.05.

Table 4a

Comparison of clinical parameters at different time periods in nonpreheated group

Follow up comparison	Surface staining	Color match/stability	Anatomic form	Fracture/retention	Marginal adaptation	Postoperative sensitivity
Baseline to 6 months	0.0002*	-	0.0431*	-	0.0077*	0.1088
Baseline to 12 months	0.0001*	0.0431*	0.0431*	-	0.0077*	-
Baseline to 18 months	0.0001*	0.0277*	0.0431*	-	0.0051*	-

P<0.05

Table 4b

Comparison of clinical parameters at different time periods in preheated group

Follow up comparisons	Surface staining	Color match/stability	Anatomic form	Fracture/retention	Marginal adaptation	Postoperative sensitivity
Baseline to 6 months	0.0117*	-	-	-	-	-
Baseline to 12 months	0.0051*	-	-	-	-	-
Baseline to 18 months	0.0051*	-	-	-	-	-

P<0.05

Table 4c shows the pair-wise comparison between the tested materials at baseline, 6, 12, and 18 months. Significant differences were observed for clinical parameters such as surface staining, marginal adaptation, color stability, and anatomic form with P < 0.05.

Table 4c

Comparison between the preheated and nonpreheated group for different clinical parameters tested

Times	Surface staining	Color match/stability	Anatomic form	Fracture/retention	Marginal adaptation	Postoperative sensitivity
Baseline	0.3173	0.3173	0.3173	-	0.3173	0.2901
6 months	0.0040*	0.2969	0.0105*	0.3173	0.0029*	-
12 months	0.0007*	0.0831	0.0105*	0.3173	0.0029*	0.3206
18 months	0.0002*	0.0437*	0.0105*	0.3173	0.0014*	0.3206

P<0.05

DISCUSSION

In vitro studies have proved that preheating the RBC enhanced the handling characteristics, decreased the film thickness, increased marginal adaptation, and decreased microleakage, but clinical studies are needed to support them.[1267]

In the present study, null hypothesis was rejected as there was a significant difference for the clinical parameters tested.

In the present study, split-mouth model was followed to obtain a balanced study design and to eliminate patient and tooth related factors.[1011]

Kim et al.,[9] in their in vivo follow-up study, concluded that FDI criteria seemed to be sensitive and precise compared to the modified USPHS Criteria, with regard to the functional properties and marginal adaptation criteria. Investigators using the FDI criteria reported it as practical, relevant, and standardized, with high intra-examiner and fair inter-examiner reliability. Hence, in the present study, an FDI criterion was used.

Jablonski-Momeni et al.[8] concluded that ICDAS II criteria have high reproducibility and accuracy for occlusal caries detection and treatment planning. Hence, in the present study, ICDAS II criteria were used along with radiographic examination.

The results of the present study showed 100% retention rates for both the preheated and nonpreheated groups, at 18-month follow-up with excellent 5.1 FDI scores. This might be due to the selective enamel etching technique and universal adhesive system used in the present study.

Single-bond Universal Adhesive contains a functional monomer such as 10-methacryloyloxydecyl dihydrogen phosphate which can form stable complexes of calcium-phosphate by chemical bonding, this was important for the quality and durability of bonding. Shaalan et al., in 1 year follow-up study on Class I cavities, reported similar results of 100% retention rate when the restorations were acid etched with 37% phosphoric acid prior to application and bonded with Single-bond Universal Adhesive System.[12]

On the contrary, Çelik et al., in 1 year follow-up study, observed loss of retention after 6 months, with a failure rate of 66%. It was suggested that poor micromechanical retention between the restoration and tooth structure in the above study was due to limited etching and inadequate removal of smear layer. Another reason might be due to different study design, as the later study was performed on noncarious cervical lesions.[13]

In the present study, marginal adaptation was found to be better for preheated RBC group compared to nonpreheated group which was statistically significant. Darabi et al. conducted an SEM study and found that preheating RBC resulted in decreased marginal gaps. Preheating RBC results in a reduction of viscosity, increases flow, which improves their ability to adapt intimately to cavity walls and margins, thus increases the ease of manipulation and less microleakge.[14] Wagner et al. concluded that the preheated treatment resulted in significantly less microleakage in the more sensitive cervical margins.[15]

In the present study, nonpreheated group showed significantly more surface staining at 6, 12, and 18 months recall visits compared to Preheated group.

Daronch et al. using infrared spectra found that preheating composite to 60°C increases DC on surface and at 2 mm depth.[16] In another in vitro study, Daronch et al. studied the polymerization kinetics of preheating RBC, they observed that there was increased molecular mobility which results in postponement of propagation, reaction termination, and autodeceleration, thereby allowing the system to reach higher limiting conversions before vitrification.[17] Lempel et al. also stated that preheating of fiber-reinforced composite to 55°C increased DC.[1] Daronch et al., in another infrared spectroscopic study, observed that an increase in polymerization temperature increased DC but only to a certain temperature limit. After this limit with subsequent raise in temperature, monomer conversion decreased due to reactant evaporation and degradation of photoinitiator.[218]

Greater formation of colorimetric degradation products and increased penetration of solvents from the oral environment into the polymer chain were found in RBC with low DC. Silane bond around the filler particles undergoes hydrolysis causing microcracks and further pigment penetration and subsequent color change due to high water sorption. Sousa et al. found that staining resistance of preheated flowable composite increased when the specimens were immersed in cola drink and grape juice for 7 days. They also observed that the samples immersed in grape juice showed the highest color change values.[19]

In the current study, on comparing both the groups, no significant changes for color stability were seen at baseline, 6, and 12 months. However, at 18-month recall, a significant color mismatch was observed in nonpreheated group. Less surface staining and greater color stability of the preheated nanoceramic RBC group in the present study can be attributed to higher DC.

In the current study, a significant loss of anatomic form was observed in the nonpreheated group. Mohammadi et al.[6] compared silorane- and methacrylate-based composites and reported that preheating increased the microhardness and elastic modulus of the silorane RBC; on the other hand, in methacrylate RBC, only microhadness was enhanced. Flexural strength values were unaffected in both the composites. Dionysopoulos et al. observed an increase in microhardness values for RBC specimens which were subjected to preheating to 55° C.[7] Similarly, in the present study, preheating might have enhanced the surface microhardness and preheated RBC group exhibited intact anatomic form throughout the recall period.

In the current study, postoperative sensitivity was found to be less for both the groups with no significant differences. Similarly, a 1-month randomized controlled clinical trial (RCT) conducted by I. Campbell et al. observed no evidence of difference in postoperative sensitivity between composites placed at room temperature and the composites preheated to 39°C.[20] Reduced postoperative sensitivity for the restorations in the present study might be attributed to the placement of SDR liner. Kaisarly et al. using microcomputed tomography concluded that application of a flowable liner of thickness from 0.5 to 2 mm led to favorable shrinkage patterns and better adaptation to cavity walls, thus acting as stress reliever.[21]

Polymerization contraction of RBC leads to shrinkage stresses. These stresses are associated with clinical complications such as cuspal deflection, debonding at the tooth restoration interface, postoperative sensitivity, and secondary caries.[22] According to Taubock Tobias T, polymerization-induced shrinkage forces were reduced to 2.6–1.6 N at 15 min after the start of irradiation when the RBC specimens were subjected to preheating to 68°C prior to photo-activation while increasing the DC.[23]

Increased concerns regarding the effect of preheating composite caused irreversible pulpal damage due to rise in intrapulpal temperature. However, Daronch et al. in their study showed that the use of preheated composite which was set to 54°C or 68°C did not produce significantly greater changes in intrapulpal temperatures.[24] El-Deeb et al. concluded that preheating of silorane RBC at temp 54°C or 68°C increased the intrapulpal temperature within critical physiological limit and had no effect on dentin micro tensile bond strength values. They also observed that the preheating temperatures were not reached inside the composite compule.[25]

Retention of temperature in the preheated RBC depends on operator's quickness, accessibility, and the distance between composite warmer and the cavity preparation. Daronch et al. reported a temperature drop of about 50% within 2 min of removing a RBC from composite preheating unit.[18]

Brunthaler et al. have suggested that failure of RBC between 0 and 5 years as early and 6–17 years as of late failures. They concluded that early failures were due to faulty technique or inappropriate indication of the restorative material or postoperative discomfort, whereas late failures are mainly due to fractures, wear and secondary caries.[3] Hence, 18 months is not sufficient time to develop variations in most clinical parameters. Therefore, clinical research studies with long-term follow-up are needed to confirm the efficacy of preheating on RBC.

Furthermore, future research should also be aimed to evaluate the clinical performance of preheated composites in other restorations such as Class II cavities and noncarious cervical lesions.

CONCLUSION

Within the limitations of this RCT of 18-month follow-up study, following conclusions can be drawn:

High retention rates were observed in both the groups

Loss of marginal adaptation, color stability, and anatomic form was found to be high for nonpreheated group which was statistically significant with preheated group

Surface staining was found in both the groups but was significantly high in non-preheated group

Significantly less postoperative sensitivity was observed in both the groups.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.