Effect of Glass Ionomer and Polycarboxylate Cements on Gingival Health of Primary Molars Restored with Stainless Steel Crown

Introduction

Preformed metal veneers, known as stainless steel crowns (SSCs), were first developed by Humphrey for pediatric dentistry in 1950. These crowns provide valuable restoration for severely damaged primary teeth (1) and last more than amalgam restorations for primary molars (2). Some studies have reported the prevalence of gingivitis to be higher around primary teeth with SSC (3, 4). On the other hand, according to some other research, the occurrence of gingivitis was not significantly different between the teeth with SSC and the controlled teeth (5, 6). Gingivitis is an inflammation that only affects the gingival margin. Its symptoms include redness, edema, and bleeding on probing (7). Some defects may result in marginal gingivitis, including poor edge adjustment, lack of complete cement removal, and irregular length of occlusogingival dimensions of the crown (8,9). Regarding the advancements in dental materials, a variety of options are available as cement (2). Four major groups of dental materials have been used for years as crown cement, namely glass ionomer cement, zinc phosphate cement, resin cement, and polycarboxylate cement (9). Among different materials, glass ionomer, zinc polycarboxylate, and zinc phosphate are used for SSCs (2). Histological evaluations revealed primary inflammatory reactions to cement near the connective tissue. These responses are usually due to the low initial pH of acid-base cement (10). According to the findings of a study conducted by Reitemeir et al.(11), the gingival health of primary molar teeth was assessed before and after receiving metal-ceramic crowns. They found that crowns with subgingival margins caused more inflammation than the supragingival ones. On the other hand, Farsi and Sharaf, in an investigation on the health of gingiva around primary molars with SSCs, reported contradictory results. They found that the spread of the crown margin did not affect the gingival tissue, while adjustment of the crown margin was significantly related to the clinical condition of the gingiva (5). The results of another study performed by Belduz Kara et al. (12) in 2014 demonstrated that the oral hygiene and health of periodontal tissue in primary molars deteriorate with time following the placement of SSCs. Moreover, in a review study by Madrigal et al. (13) in 2014, the predisposing factors for gingivitis related to SSCs were evaluated. According to this review, there is not sufficient evidence regarding the role of crown adjustment, remaining cement, SSCs, and their marginal spread as predisposing factors for gingival disease in children. It can be concluded that there are contradictory views about the influencing factors on gingival inflammation around restored teeth with SSCs. Moreover, different cement properties, such as solubility, microleakage, chemical components can have various effects on the surrounding gingiva. Therefore, the present study aimed to evaluate the effect of glass ionomer and polycarboxylate cement used in SSCs for primary molars on the gingival health of these teeth.

Materials and Methods

This double-blind randomized clinical trial was performed on 34 children within the age range of 4-7 years, who were referred to the Dentistry Faculty of Qazvin University of Medical Science, Qazvin, Iran for bilateral SSCs in one jaw. This study was approved by the Ethics Committee of Qazvin University of Medical Sciences (IR.QUMS.REC.1394.267). At the beginning of the study, the objectives and procedures were explained for the parents of the subjects, and written informed consent was obtained from the legal guardian of the participants. The inclusion criteria were as follows: 1) age range of 4-7 years, 2) lack of known systemic diseases, mental disorders, or physical disabilities that may interfere with the person’s adherence to the principles of oral hygiene, 3) not having rotation or improper occlusion in the intended teeth, and 4) having two defective teeth with similar numbers in one jaw. Before the study, the parents were instructed regarding the principles of oral hygiene, such as brushing the teeth using a horizontal scrub technique and applying dental floss. The parents were requested to brush the teeth of their children twice a day (in the morning and before sleep at night) and use dental floss every night for cleaning the teeth. The hygiene level was determined using the Simplified Debris Index (DI-S), according to Silness-Löe Index (14). It was scored based on four levels of 0= no plaque, 1=soft debris within 1/3 of the tooth surface, 2=soft deposit beyond 1/3 of the tooth surface, but within 2/3 of the tooth surface, and 3=soft matter beyond 2/3 of the tooth surface. Preparation of the teeth was carried out by a resident of pediatric dentistry under the supervision of a pediatric specialist. Following the initial examination of occlusion, suitable regional anesthesia was performed as an inferior alveolar nerve block for the mandible and as buccal and palatal infiltration for the maxilla. In order to provide ideal isolation, a rubber dam was used. Afterward, the occlusal surface was cut by dental burs (#169 L; SUNSHINE, CA, USA) with a cusp slope of 1-1.5 mm, and the pulp therapy was applied as required. Moreover, the proximal region was cut by diamond burs (SUNSHINE, CA, USA) at a distance of 1 mm from the adjacent tooth and a feather-edge finish-line. Next, all angles were blunted by the sides of the burs. For example, the occluso-buccal and lingo-buccal angles were blunted at angles of 30-45°. At this stage, a suitable SSC was selected (3M ESPE, St. Paul, USA) through trial and error. The smallest SSC that could restore proximal contacts was selected in this study. The SSCs were first placed from the lingual side with pressure on the buccal side. Following the evaluation of the occlusion, correction preparation was performed if the veneer was not at the same level as the marginal ridge of the adjacent tooth. In addition, the over contoured or high margins were corrected when the gingival tissue around the margin was bleached. The latter procedure was practiced using special scissors, ball, and socket plier. When the crown was placed, the gingival margins were examined using an explorer for finding regions with unsuitable fitting. A suitable crown should have been placed 1 mm in the gingival sulcus. Afterward, the crowns were removed, the rubber dam was evacuated, and the crowns were placed again for the final evaluation of the occlusion. Moreover, the crowns were polished if they were cut. Next, the crowns were washed, dried, and prepared for the cementation step. The SSC on each side was randomly stuck by glass ionomer cement (GC gold label luting and lining cement, GC Corporation, Tokyo, Japan) and polycarboxylate cement (Master Dent, Dentonics Inc., NC, USA) using random allocation software (version 2.0). Two-thirds of the crowns were filled with the chosen cement and placed on the clean, dry tooth. Prior to the final setting, the occlusion was re-examined and the extra cement was then removed from the sulcus by water spray and dental floss at interproximal regions. The type of cement, jaw, tooth number, and crown were all recorded in checklists. The children were followed-up after six months, and their gingival health was assessed using the gingival index (GI) in the follow-up session by a blind pedodontist. For this purpose, gingiva of the intended tooth was evaluated regarding color, presence/absence of edema, and bleeding on probing. The health or inflammation of the gingiva was determined based on Silness-Löe Index with four levels of 0=normal gingiva; 0-1=mild inflammation, no bleeding on probing, change in color and edema; 1-2=moderate inflammation, bleeding on probing, redness, edema, and glazing; and 2-3=severe inflammation, spontaneous bleeding, marked redness and edema.

 In order to examine the crown margin adjustment, the explorer was moved from the gingival to the occlusal direction. The adjustment was considered weak or favorable in case the explorer stuck or did not stuck, respectively. The presence or absence of extra cement at the buccal surface and lingual margin of the crown was determined through observation and examination by an explorer (“Yes” or “No”) (Table 1).

 Table I. Clinical criteria used for evaluation of SSC

  Statistical analysis

The descriptive statistics, namely the Wilcoxon Rank test, Chi-square test, binary logistic regression with entry method were performed for statistical analysis. In the regression model for the dependent variables, the normal status category represents the reference group. The SPSS software (version 25.0) (25 IBM Corp. IBM SPSS Statistics for Window, Armonk, NY) was used for analyses.

Results

In the present study, 68 primary molars of 34 children (18 females [53%] and 16 males [47%]), within the age range of 4-7 years, were investigated. There were 24 maxillary teeth, including 10 first molars and 14 second molars, and 44 mandibular teeth, including 18 first molars and 26 second molars (Table 2).

Table II. Tooth distribution according to the arch and type

The plaque index for the primary molars was measured before and after the crowning. Prior to the intervention, 16 (23.5%), 24 (35.3%), and 28 (41.2%) teeth had good, moderate, and weak plaque indices, respectively. After the crowning, 22 (32.4%), 39 (57.4%), and 7 (10.3%)

teeth had good, moderate, and weak plaque indices, respectively; the latter difference was statistically significant (Table 3).

Table III. The plaque index for primary molars before and 6 months after SSC placement

*Wilcoxon Ranks test

Based on the results of the present study, in the gingiva adjacent to the crowns cemented with glass ionomer, 11 (32.4%) teeth were normal, while 13 (38.2%), 9 (26.5%), and 1 (2.9%) teeth had slight, moderate, and severe inflammation, respectively. Furthermore, in crowns cemented with polycarboxylate, the gingiva was healthy in 9 (26.5%) teeth, while it was affected by

slight, moderate, and severe inflammation in 6 (17.6%),

15 (44.1%), and 4 (11.8%) teeth, respectively. Considering the distribution of data and possibility of a more accurate interpretation, the variable was dichotomized and defined as “normal” (normal and mild) and “with gingivitis” (moderate and severe) (Table 4).

Table IV. Gingival situation before and 6 months after SSC placement  

*Chi-Square test

Logistic regression analysis was used for evaluating confounding factors, including gender, tooth number, and jaw. The results indicated that gender and tooth number (first or second molar) did not exert any significant effects (P=0.674 and P=0.942, respectively).

On the other hand, cement type and jaw (maxilla or mandible) had significant effects (P=0.022 and P=0.007, respectively). Therefore, normal GI was more probable in the maxilla, compared to the mandible. Moreover, we found that the rate of normal GI was significantly higher in teeth with glass ionomer cement, compared to polycarboxylate cement (Table 5).

Table V. Odds ratio (OR) and 95% confidence intervals (CI) for gingivitis