Effect of Matrix Systems and Filling Materials on Proximal Contacts in Primary Molar Restorations: An In vitro Study

Aim: This study evaluated the influence of the matrix system and filling material on the proximal wall morphology and contact tightness in Class II restorations of primary molars.

Place and Duration of Study: Department of Paediatric Dentistry, Faculty of Dental Medicine, Medical University of Sofia, Bulgaria, between September 2024 and December 2024.

Methodology: On 240-second primary molars, occlusal-medial and occlusal-distal class II cavities with dimensions of 3x4x2 mm (buccolingual, occlusal-gingivally, and mesiodistally) were prepared. The teeth were then divided into six groups (40 teeth each) and were restored with different filling materials (compomer or bulk fill composite) and different matrix systems (sectoral and circumferential). The contact tightness of the proximal restorations was examined by inserting a different number of metal flat matrices with a thickness of 0.05 mm. Visually, the surface profile of the contact morphology was assessed and classified as flat, convex, or concave. Their marginal adaptation was also evaluated according to the following criteria: presence of a step and/or voids. The examination was performed under a dental microscope.

Results: The palodent matrix system provided the tightest contacts to first primary molars when using compomer material, while the myJuniorKit system excelled with bulk-fill composites. For the first permanent molars 36 and 46, the junior matrix system consistently provided the tightest contacts, irrespective of the restorative material. A convex restoration profile is typically observed with the myJunior matrix system, while a flat profile is usually seen with the circumferential matrix system. There is a risk of void formation when using condensable filling materials but not when using bulk-fill material.

Conclusion: The effectiveness of the proximal contour of primary teeth restorations is influenced more by the type of matrix system used than by the filling material or filling technique. Using sectional matrix systems designed explicitly for primary teeth (MuJuniorKit) significantly improves the proximal contacts of Class II composite restorations in primary molars. Circumferential matrices have a higher risk of edge formation than sectional matrices, and a higher risk of void formation is seen with compomers and layering restoration techniques.