One of the biggest challenges encountered by even the most skilled clinicians while placing Class II restorations is producing tight proximal contacts and obtaining anatomically accurate proximal contours. Proximal contact tightness (PCT) is a physiological dynamic entity of multifactorial origin that is largely affected by tooth type, location, time of day, patient position, mastication and restorative procedures. A significant variation in proximal contact is also seen both inter- and intra-individually. The use of pre-contoured circumferential or sectional matrix bands used with a separation ring has been shown to attain good contact tightness due to the interdental separation applied by the ring during restoration. There have been numerous studies conducted on the proximal contact tightness evaluation on teeth restored using composites and amalgam previously. The aim of this study was to evaluate proximal contact tightness between two newer restorative materials, i.e. Cention N (Ivoclar vivadent) and Zirconomer Improved (Shofu Inc. Kyoto, Japan), using dental floss, under the FDI criteria.
Materials and methods
Eighty Nissin typodont posterior teeth were used in this study. In all the teeth, mesio-occlusal cavity preparation was done with a high-speed handpiece. The teeth were equally divided into two groups (40 each). Group 1 (n=40) – Restored with Cention N (ivoclar vivadent) Group 2 (n=40) – Restored with Zirconomer Improved (Shofu).All the restorations were placed by the operator and proximal contact tightness was evaluated using dental floss and the scoring was given under the FDI criteria.
The results were analyzed using Statistical Package for Social Sciences (SPSS- version 21). Frequencies and percentages were calculated for the scores assigned to both restorations. Chi square test was used to test the significance of difference between the two restorative material groups. P-value of ≤ 0.05 was considered statistically significant.
Proximal contact tightness was clinically excellent (score 1) in 69% of the restorations with Cention N, as compared to Zirconomer Improved, which showed clinically excellent (score 1) proximal contact tightness in 31% of the restorations. Score 2 (clinically good proximal contact tightness) was seen in 34% of the Cention N restorations and 66% of the Zirconomer Improved restorations. The difference was statistically significant (p= 0.015) between the two groups.
One must appreciate the role of a proximal contact in the natural dentition to acknowledge the importance of reproducing its shape and tightness during tooth restoration. The role of the proximal contact in protecting the periodontium from damage due to food impaction is very important. Loose proximal contacts predispose to food impaction, periodontal problems, tooth migration and carious lesions. On the other hand, trauma to gingival tissue has been seen when extreme pressure is applied to pass dental floss through tight contacts. An important pre-requisite to attaining interdental integrity is obtaining acceptable contact areas with adjacent teeth and re-establishing optimal physiologic contact between adjacent proximal surfaces.
According to Loomans et al, Class II restorations placed with a combination of sectional matrices and separation ring produced stronger proximal contact than when a circumferential matrix system was used. The Tooth Pressure Meter device, (TPM) described by Dörfer and Loomans can precisely determine the proximal contact tightness. The PCT is measured as the maximum frictional force (N) applied on a 0.05 mm thick metal strip upon removal from the interproximal area in an occlusal direction. Since this method was not commercially available, we were forced to access the result using traditional method. With the decline in popularity of amalgam in recent years and an increased demand in tooth colored restorations, there is a need for equally strong & bondable materials. Two such recently introduced materials include Zirconomer Improved and Cention N.Cention N (Ivoclar Vivadent; Schaan, Liechtenstein) is a tooth-colored, basic filling material for bulk placement in retentive preparations with or without the application of an adhesive. It is an “alkasite” restorative which is a new category of filling material, like compomer or ormocer and is essentially a subgroup of the composite resin.
Cention N is a UDMA-based, self-curing powder/liquid restorative with optional additional light-curing. The liquid contains dimethacrylates and initiators, whereas the powder comprises of various glass fillers, initiators and pigments. It is radio opaque and contains alkaline glass fillers capable of releasing fluoride, calcium and hydroxide ions. The special patented filler (Isofiller) acts as a shrinkage stress reliever due to its low elastic modulus and reduces polymerization shrinkage and microleakage. It exhibits a high polymer network density and degree of polymerization over the complete depth of the restoration because of the sole use of cross-linking methacrylate monomers in combination with a stable, efficient self-cure initiator. Cention N offers a substitute for amalgam and also fulfills the need for an esthetic bulk fill material in the posterior region. A study conducted to compare proximal contact tightness between two different restorative materials, charisma composite and cention N, showed that Cention N produces proximal contact tightness same as that of a composite material used.
Zirconomer is a recently introduced glass ionomer formulation to overcome the disadvantages of traditional GIC formulations. It has the strength of amalgam along with the beneficial effects of GIC and eliminates the hazardous effect of mercury; hence, it is also termed as white amalgam. Zirconomer Improved consists of novel nano-sized zirconia fillers that enhance the material translucency for a closer shade match to natural teeth with superior handling characteristics for a simple, easy and fast bulk placement.
Attaining acceptable proximal contacts has been claimed to be easier when using high viscosity or ‘packable’ restorative materials. As shown in the results of the current study, the proximal contact tightness in 69% of Cention N restorations having were graded under score 1 and 66% of the Zirconomer restorations with score 2. The difference was statistically significant (p= 0.015) between the two groups. This can be attributed to the difference in viscosity between two materials and needs further evaluation. However, both Cention N and Zirconomer Improved were under the clinically acceptable (score 1 and 2) categories.
Within the limitations of the present study, both Cention N and Zirconomer improved when used in Class II restorations, offer clinically acceptable proximal contact tightness. Although, a well-designed randomized controlled study with long-term follow-up and clinical studies are required to be performed to give valid evidence on the proximal contact tightness.