Effects of Color and Glitter on the Removable Space Maintainer

Introduction

Premature loss of teeth may occur as a result of certain problems, such as caries, abnormal resorption, systemic diseases, and trauma (1, 2). Early loss of the primitive tooth may lead to the migration of the existing teeth and loss of arc space (2-4).Loss of arc space can lead to impairment in permanent teeth configuration, such as crowing, supra-eruption, and impaction (5). In order to avoid these problems, a space maintainer is needed to keep sufficient space for the permanent teeth to erupt and maintain a well-aligned position (3, 6). The principal function of a space maintainer is the guidance of the eruption of the permanent teeth and avoidance of crowding or supra eruption (7). A space maintainer should maintain the mesiodistal space and easily fabricated and withstand functional forces (1). The usage of space maintainers may prevent a more complex orthodontic treatment in the future (6). There are two major types of space maintainers, namely fixed and removable space maintainer (RSM) (3, 6, 8). The most commonly used RSMs are simple acrylic and removable partial dentures. Removable partial dentures help mastication, improve esthetics, and prevent unwanted tongue habits (3). However, children in the primary dentition ages may have difficulties using and taking care of their removable maintainers. Since they may lose their devices, acrylic maintainers are prone to damage (3).

In order to promote the adaptation of young patients to their devices, there is an increasing demand for colored or decorated devices. To fulfill this demand, color pigments, glitter, or other decorations have been used widely in the dental market (4). However, a review of the related literature shows that studies on the effects of pigment or glitter addition to polymethyl methacrylate (PMMA) are very limited. PMMA has become the most common denture base material for decades, compared to other available materials. The reason for this interest in PMMA is its features, such as easy manipulation, satisfactory esthetics, and low price (9, 10). However, its mechanical properties impose limitations on the material (11, 12). Pediatric or orthodontic appliances are prone to crack or fracture due to occlusal force and fatigue caused by insertions and extractions (14). In the previous literature, researchers investigated the survival and success of both removable and fixed space maintainers (14-16). The common idea in these studies was that gender and age did not affect the survival of the space maintainers. Tulunoglu et al. (14) and Martu et al. (15) stated that deformation of retentive parts and fractures were the most common causes of space maintainers failure. Furthermore, Quedimat et al. (16) declared that more fractures were observed in removable partial dentures, followed by a lower lingual holding arch. Beldiman et al. (17) in their study compared the mechanical properties of different space maintainers and stated that removable space maintainers were weaker than the fixed ones. Despite the fact that patient education and close observation may prevent any probable complications, any chance to decrease the risk factors would be advantageous (2). The null hypothesis of the study was that adding color and glitter would not affect the flexural strength of the PMMA.

Materials and Methods

A total of 40 PMMA specimens (64 mm×10 mm×2.5 mm) simulating a retainer were prepared and divided into 4 groups (n=10). For all groups, PMMA resin (Orthocryl, Dentaurum, Germany) was mixed at room temperature (22°C) according to the instructions provided by the manufacturers. Group 1 was prepared with clear resin and served as the control group. Group 2 was prepared with clear resin and glitter (Orthocryl® Disco Glitter, Dentaurum, Germany) with a ratio of 0.5:100 (glitter/powder). Group 3 was prepared as colored (red) by adding color concentrate (Orthocryl® Color Concentrate, Dentaurum, Germany)  with a ratio of 1:30 (coloring concentrate/liquid). Group 4 was colored similar to Group 3 and glitter was added as well. The specimens were packed into stone molds and brass flasks. Prior to packing, the molds were immersed in warm water for 15 min, until no more air bubbles emerged from the plaster. The resins were polymerized at 46°C for 25 min in a pressure chamber (Polimer 180, Zhermack SpA – Badia Polesine, Italy) under 32 psi pressure.

After the polymerization of resins, the excess material was removed with a tungsten carbide bur (Euro Carbide Bur; Dedeco, NY, USA) at 15.000 revolutions per min, and the surfaces were finished with 200 and 600 grid sandpapers. The specimens were thermocycled at 5°C and 55°C for 1000 times (Esetron, Mechatronics, Ankara, Turkey). The cycle periods were 15 sec for hot and cold water and 30 sec of dwell time.

A three-point flexure test (ISO 1567) was performed to measure the flexural strength of the specimens. The specimens were placed in a test machine (Esetron Mecathronics, Ankara, Turkey) on a test rig with cylindrical supports which were 3.2 mm in diameter and 50 mm apart. The load was applied to the specimens at a crosshead speed of 5 mm/min. The fracture force was recorded in Newton (N) and flexural strength (Fs) was calculated with the formula of ”Fs = 3PL/2 bd²” where P was the maximum load, L was span length, b was specimen width, and d was specimen thickness.

Statistical analysis was conducted in SPSS software (version 19). The flexural strength was analyzed using the Kruskal–Wallis test. The Conover-Iman test of multiple comparisons was performed to detect the differences among the groups. In all the tests, a P-value of 0.05 was considered statistically significant.

Results

The mean flexural strength values of tested resin groups are displayed in Figure 1. The Kruskal–Wallis test showed that there were significant differences among the groups regarding flexural strength (P=0.001). Iman Conover pairwise comparison test showed that the clear-glitter group (40,76±6,5447130 MPa) was significantly different from the clear group (50,67±5,50 MPa) (P=0.001). Besides, other groups (red color 59,40±10,07 MPa and red-glitter 47,96±9,047 MPa), did not have significant differences with eachother (P>0.05). (Table I)

Table I.  Mean, standard deviation, flexural strength, and minimum and maximum values of the samples

Figure 1. Boxplot graphic of the studied polymethyl methacrylate