One-year clinical evaluation of bulk-fill composite resin restorations plasticized by preheating and ultrasonics: A randomized clinical trial.

Introduction: Bulk-fill composite restorations displayed substantial annual failure related to imperfect marginal adaptation. Although preheated composites improved, marginal adaptation demonstrated early loss of plasticity. A new technique of ultrasonics plasticization was used for fabricating restorations. Aim: The aim of this study was to assess the clinical behavior of bulk-fill composite resin restorations plasticized by preheating and ultrasonics. Methodology: Randomized split-mouth double-blinded clinical trial was designed. Bulk-fill composite resin (Tetric N-Ceram Bulk Fill Ivoclar Vivadent products, Delhi) was used to fill 56 cavities. In 28 restorations, composite resin was plasticized by preheating in composite warmer (Delta Co., India) and remaining were plasticized with modified ultrasonic-retreatment tip-RT No 2 (Cricdental, India). Clinical follow-up assessments were done at 6 and 12 months using Ryge's criteria. Mann-Whitney U-test was used for statistical analysis with P < 0.05 and effect size of 0.61.
Results: Hundred percent clinical success with ultrasonic plasticized group and 95.2% success with preheated composite resin group were observed without statistical significance.
Conclusion: The ultrasonics plasticization of composite resin demonstrated comparable results with that of preheated composite resin after 6- and 12-month recall. Use of vibration energy utilizing the thixotropic effect might have resulted in better clinical performance. Copyright:

INTRODUCTION

Composite resin restorations have played a major role in providing esthetics and self-esteem to the patients. A retrospective longitudinal study of 5–20 years has reported a mean survival time of 11 years 7 months.[1]

Bulk-fill composite restorative resin was introduced to reduce the chairside time along with favorable properties such as decreased polymerization shrinkage, reduced cuspal deflection, and optimal bond strength.[2] However, a 10-year follow-up clinical trial of bulk-fill composite resin restorations displayed 23% failure rate.[3]

To improve the adaptation of viscous bulk-fill composite resin, preheating of resin was introduced.[456] Clinical evidence is scanty regarding the beneficial effect of preheating on restoration's quality and durability.[7] In this method, a temperature drops of 50% after 2 min and about 90% after 5 min were observed after removal of composite resin from the warmer.[8] Hence, clinician must work faster, compromising the creativity in sculpting of an esthetic biomimetic restoration.

A bulk-fill proprietary resin including modifiers which get activated by a specific sonic handpiece was developed to improve material adaptation to cavity wall.[9] This requires special equipment and corresponding resin. This principle was simulated in the present study for the plasticization of composite resin with the use of customized ultrasonic tip to enhance the adaptation between composite resin and prepared tooth surface.

The objective was to evaluate the clinical behavior of high viscosity bulk-fill resin composite restorations plasticized by preheating or ultrasonic application in posterior teeth using Ryge's criteria.[10] (modified United States Public Health Service [USPHS] criteria).

The null hypothesis assumes that clinical behavior of composite resin restorations plasticized by preheating and ultrasonics do not differ with statistical significance.

METHODOLOGY

The trial obtained ethical clearance from the institute with ref no VDC/IEC/2019/05 and was registered in http://www.ctri.nic.in/with ref no CTRI/2020/09/027648 from March 2019– September 2019. Patients requiring Class I or Class II restorations from the Department of Conservative Dentistry and Endodontics were enrolled in the trial. Patients signed an informed consent after explanation of risks and benefits of trial. The code of ethics of the World Medical Association (Declaration of Helsinki) was followed during the clinical trial. The trial design was randomized split-mouth double-blinded, wherein patients and observers were blinded to the protocols. The clinical trial design followed recent CONSORT recommendations.

Sample size considerations

The sample size was calculated using G * power software based on the previous sample size calculations performed in similar study.[11]

The calculation was based on an actual power size of 0.817, an alpha level of 0.05, a desired power of 80%, and the effect size of 0.61. The desired sample size was 42.

Fifty-six cavities from 28 patients were restored. Excess of seven patients was enrolled to compensate for any unexpected dropouts [Figure 1].

Figure 1

CONSORT flowchart showing flow of participants along the study

Inclusion criteria

Patients of age 18–45 years

Teeth with opposing teeth in occlusion

Asymptomatic vital teeth

A healthy periodontium

Moderate size cavities.

Exclusion criteria

Xerostomia and bruxism

Unerupted or partially erupted tooth

Fractured or visibly cracked teeth.

Class I or II restorations were placed in every patient. The samples were randomly divided using computer generated randomization (Research Randomizer). Following the split-mouth design, 50% of the samples were restored with preheated composite resin and remaining with ultrasonically plasticized composite resin.

Clinical procedure

Restorations were placed by a calibrated operator. Clinical protocol was carried out under rubber dam isolation (GDC Dental Instruments, India). Caries were excavated using a spoon excavator (GDC Dental Instruments, India). The conservative cavity was prepared using diamond points (Mani Inc., Japan) with a high-speed handpiece. Selective etch and rinse (N-Etch, Ivoclar Vivadent, Delhi, India) followed by bonding (N-Bond, Ivoclar Vivadent, Delhi, India) protocol was carried out as per manufacturer's instructions.

Group I–Bulk-fill composite (Tetric N-Ceram Bulk Fill), Ivoclar Vivadent products, Delhi) (LOT no: X20834) was preheated to 60°C in composite warmer (Delta Co., India) for 5 min and inserted.

Group II-Bulk-fill composite (Tetric N-Ceram Bulk Fill), Ivoclar Vivadent products, Delhi) (LOT no: X20834) was inserted, and ultrasonic plasticization was done by placing modified ultrasonic tip (RT No– 2, Cricdental, India), in ultrasonic handpiece (Woodpecker, Guilin, China), over the composite material for 1 min at medium energy. The ultrasonic tip was modified by slightly rounding off the tip.

In both groups, the material was contoured using suitable instrument, and polymerization was done with a light-emitting diode (Woodpecker, Guilin, China) with intensity (1000 mW/cm2) for 40 s. Finishing and polishing of the restorations were done with fine-grit diamond points (Mani Inc., Japan) and Super-Snap Mini Kit finishing and polishing discs (Shofu, India).

Clinical evaluation

At the end of 6 months and 1 year, the restorations were assessed. Two clinicians, who were not the part of clinical trial, rated the restorations as per criteria given by modified USPHS[11] under dental operating microscope (Labomed, India). Calibration of the clinical evaluators was done before the study by combined evaluation of twenty direct composite restorations (Cohen kappa value >0.78). Ideal clinical situation was rated as Alpha, clinically acceptable as Bravo, and unacceptable as Charlie.

Statistical analysis

The data were entered into a spreadsheet (Excel 2013, Microsoft, Seattle, WA, USA) to calculate the descriptive statistics and analyzed using statistical computer software (SPSS version 23, Chicago, IL, USA). As the results yielded ordinal structural data, only nonparametric statistical procedures were used. The difference in clinical behaviors of the restorations at 6 months and 1 year was compared with the Mann–Whitney U-test. The confidence level was set to 95% (P < 0.05) with effect size of 0.61.

RESULTS

Out of 28 patients, seven patients did not report for recall because of the COVID-19 pandemic. Hence, 21 patients with 42 restorations were evaluated who met the required sample size.

All restorations received Alfa ratings at baseline in both groups. Two restorations in preheated group received Bravo ratings (9.5%) for surface texture at 6 months, and one restoration received Charlie rating (4.8%) for postoperative sensitivity, marginal adaptation, anatomic form, and retention at 6 months. Statistically significant difference was not there (P = 0.152) between follow-ups in two groups. There was no statistical difference (P = 0.317) between follow-ups in terms of postoperative sensitivity, marginal adaptation, anatomic form, and retention for prewarmed technique [Table 1].

Table 1

Mann-Whitney U-test software used: SPSS version 23.0

USPHS criteria	Code	6 months			12 months
		Prewarmed, n (%)	Ultrasonic, n (%)	P	Prewarmed, n (%)	Ultrasonic, n (%)	P
Color match	Alpha	21 (100.0)	21 (100.0)	1.000	21 (100.0)	21 (100.0)	1.000
	Bravo	-	-		-	-
	Charlie	-	-		-	-
Marginal adaptation	Alpha	20 (95.2)	21 (100.0)	0.317	20 (95.2)	21 (100.0)	0.317
	Bravo	-	-		-	-
	Charlie	1 (4.8)	0		1 (4.8)	0
Surface roughness	Alpha	21 (100.0)	21 (100.0)	1.000	19 (90.5)	21 (100.0)	0.152
	Bravo	-	-		2 (9.5)	-
	Charlie	-	-		-	-
Anatomic form	Alpha	20 (95.2)	21 (100.0)	0.317	20 (95.2)	21 (100.0)	0.317
	Bravo	-	-		-	-
	Charlie	1 (4.8)	0		1 (4.8)	0
Retention	Alpha	20 (95.2)	21 (100.0)	0.317	20 (95.2)	21 (100.0)	0.317
	Bravo	-	-		-	-
	Charlie	1 (4.8)	0		1 (4.8)	0
Postoperative sensitivity	Alpha	20 (95.2)	21 (100.0)	0.317	20 (95.2)	21 (100.0)	0.317
	Bravo	-				-
	Charlie	1 (4.8)	0		1 (4.8)	0
Secondary caries	Alpha	21 (100.0)	21 (100.0)	1.000	21 (100.0)	21 (100.0)	1.000
	Bravo	-	-	-	-
	Charlie	-	-	-	-

USPHS: United States Public Health Service

The statistical comparison between the results at 6 and 12 months of clinical service did not show a statistically significant difference (P > 0.05) between preheated and ultrasonic plasticization techniques.

DISCUSSION

Literature reveals that bulk-fill composite resins exhibit marginal gaps like that of conventional resin composites.[1213] Hence, this study was planned to minimize the marginal gap which might have detrimental effects on the success of composite resin restorations.

Results of laboratory testing cannot be projected in correlating with the clinical performance of restorations. The complex dynamic environment of oral cavity has tremendous effects on marginal seal of restorations. Hence, research, in terms of randomized clinical trials, is recommended. The split-mouth design minimizes bias of oral dynamics as the patient serves as his/her own control, which can increase statistical efficiency.[14]

After 12 months of clinical service, ultrasonic plasticization group showed better results than those of preheated group without statistical significance. At the end of 1 year, restorations of both techniques were retained. No difference in the response was observed between male and female patients. Some studies reported that restorations in premolars show significantly better survival rates than those in molars.[15] However, the findings of the present study do not confirm these results.

In the present clinical trial, 14.3% of restorations represented compromised behavior. One restoration from preheated group was scored Charlie for marginal adaptation, postoperative sensitivity, anatomic form, and retention after 6 months. Two restorations from preheated group demonstrated Bravo for surface roughness. Preheating is claimed to improve the properties of viscous composite formulations. in vitro studies have published mixed results regarding change in the properties of the bulk-fill materials by preheating composite resin.[1617] Scientific literature reported very few in vivo studies regarding preheated composites. A clinical trial for evaluating postoperative sensitivity with preheated composites has reported very low sensitivity.[18] Controversial reports were published in literature regarding the beneficial effects of preheated composite resins. A systematic review reported improved mechanical and physical properties with a caution that clinical studies are lacking to confirm the same.[7]

Effect of preheating of composites on marginal adaptation when evaluated with SEM revealed better marginal adaptation with some gaps which could be attributed to rapid drop in composite temperature during handling.[5] Another SEM evaluation reported that marginal gap observed in enamel was 0.70–0.80 μm and 5.16–5.47 μm in dentin.[4] Marginal gap and internal adaptation of bulk-fill composite resin were influenced by viscosity. The gap-free margins observed in enamel declined after thermal cycling.[19] This indicates that marginal gap though less persists. This must have compromised behavior of few restorations in the present clinical study.

Restoration rated as Charlie was retreated. Restorations rated Bravo for surface roughness were refinished and polished.

Application of ultrasonics to mechanically energize restorative material is reported as another option. In the ultrasonic plasticized restoration group, 100% clinical and radiographic success was observed during 6- and 12-month evaluation period.

Literature shows better in vitro and in vivo success with composite restorations activated with sonic energy with special composite resin formulation and specialized equipment.[9] High viscosity bulk-fill composite resins activated with sonic energy demonstrated acceptable clinical performance, because of high amount of inorganic filler and improved adaptation due to its low viscosity caused by sonic activation.

A preliminary observation evaluated marginal adaptation by indirect application of ultrasonic activation of composite restoration by applying a plastic-coated tip (PCS-Set, EMS) onto the buccal surface of the tooth after composite placement. The study concluded that ultrasonic activation of composite resin improved the marginal adaptation.[20] In another study, Class I inlays were cemented with various viscous composite resins with manual and ultrasonic activation and compared the interface. Authors concluded that the ultrasonic activation could make highly filled viscous composite resin suitable for cementation without affecting filler distribution or film thickness.[21]

The tested technique in the present study was ultrasonic plasticization of restorative material that combines the advantages of a flowable and universal resin composite without the need for any additional capping layer and special equipment. It is speculated that the use of vibration energy utilizing the thixotropic effect may cause changes in the filler/matrix distribution.[21] A recent study reported that the polymerization quality of sonic-activated composite resin was improved compared to that of low-viscosity bulk-fill composite resin.[22]

At the end of 1 year, all the restorations were satisfactory and considered as ideal, receiving predominantly Alfa scores for all parameters analyzed. No significant differences between the preheated and ultrasonic techniques were observed in the clinical behavior. Hence, the null hypothesis was accepted.

The external validity of this study was influenced by the fact that it was conducted at a dental college and that the same dentist placed all restorations. It is, therefore, not possible to state with confidence that the findings of this clinical trial would be replicated in everyday dental practice. However, the protocol followed can be recommended as good clinical practice.

The limitations of this study are limited number of patients and short observation period. Hence, long-term prospective clinical trials are required to confirm the acceptable clinical behavior of bulk-fill composite resins plasticized with preheating and ultrasonics.

CONCLUSION

From the present clinical trial, the following conclusions can be drawn:

1-year evaluation demonstrated satisfactory results for preheated and ultrasonically plasticized composite restorations without significant difference statistically

Preheated composite resin restorations exhibited 95.2% of clinical success. 4.8% restorations demonstrated Charlie criteria and 9.5% demonstrated Bravo criteria

Ultrasonic plasticization group demonstrated 100% clinical success with Alpha criteria.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.