Clinical success and its associated influencing factors in the placement of resin-bonded strip crowns on primary anterior teeth in children under general anaesthesia: a 1-year retrospective study

2.1 Data collection

The RSCs were placed on the teeth of children who received dental treatment under DGA at Guangzhou Women and Children’s Medical Center between January 2013 and December 2016. Children who had been followed up for at least 12 months were included in this study. All treatments were completed by two certified paediatric dentists, and all operators used the same materials and treatment protocols.

The inclusion criteria were as follows: (1) had indications for DGA [13]; (2) had at least one anterior tooth restored with an RSC; and (3) had a postoperative follow-up duration of no less than 12 months. The exclusion criteria were as follows: (1) teeth affected by caries or trauma with less than 1/3 of the crown structure remaining; (2) teeth with periapical inflammation; and (3) tooth exfoliation time of less than one year.

An Excel spreadsheet was used to record information by consulting the electronic medical records system. Factors potentially related to treatment failure were investigated, including individual and clinical characteristics: sex (boys or girls), age, arch type (in the upper or lower jaw), tooth position (primary incisors, primary lateral incisors and primary canines), and number of carious surfaces of the tooth (1–2 or 3–4 surfaces). The patients’ follow-up time and evaluation of RSCs during follow-up visits were also recorded. The number of carious surfaces was counted using preoperative photographs (Fig. 1).

Fig. 1.Preoperative photographs of the patient. (a) Preoperative frontal view showing that the labial surfaces of 53–63 and 73–83 all had caries; the mesial surfaces of 52, 62, 63, 71 and 81 had caries; and the distal surfaces of 52, 51, 61, 62 and 82 had caries. (b) Maxillofacial view showing that the lingual surfaces of 53–63 had caries. (c) Mandibular view showing no caries on the lingual surfaces of 73–83.

2.2 Restorative procedure

The decayed dentin of the anterior tooth was removed, the infected dentin near the medulla was retained, and 0.5~1.0 mm of dental tissue was evenly removed at the contact point. We then selected the appropriate strip crown (Kids Crown, Korean), trimmed and tested it. The restorative procedures were performed under cotton isolation. A thin layer of Calcimol LC (VOCO GmbH, Cuxhaven, Germany) was used in the deep and moderate cavities. Root canal treatment was performed on teeth with pulpitis. Under rubber dam isolation, the canal was mechanically prepared using a series of 21 mm long K-type endodontic files up to file #40. The working length was estimated using preoperative radiographs. The root canals were then irrigated after each file was prepared with 3% hydrogen peroxide and saline and dried with paper points. Vitapex paste (Neo Dental Chemical Products Co. Ltd, Tokyo, Japan) was used to fill the root canal, and glass ionomer cement (Fuji IX, Japan) was placed at the bottom. The strip crown was filled with composite resin (GC Phantom series, colour A2, Japan). Clearfil SE Bond (CSB; Kuraray Co. Ltd., Osaka, Japan) Primer was applied for 20 s and air-dried for 5 s, and the bonding agent was then applied using a microbrush and light-cured for 10 s. The strip crown was inserted into the tooth and fixed in the correct position. Excess resin was removed with the probe, and each tooth surface was cured in the light for 20 s. The cotton and strip crown were removed. Finally, the occlusion was checked. Typically, restorations require minimal finishing. If needed, the shape or reduction of excessively long incisor edges was performed using composite finishing disks and strips (Fig. 2).

Fig. 2.Preoperative and postoperative comparisons of RSC restoration. (a) Before RSC restoration, all the primary anterior teeth suffered from varying degrees of dental caries. (b) After the RSCs were restored, all the primary anterior teeth achieved a good appearance, smooth surface, uniform colour, and appropriate occlusal.

2.3 Evaluation method

The evaluation method for the filling material was recorded in an outpatient system. The patient was evaluated by one of two paediatric dentists, and both dentists used the same evaluation criteria, which were based on Ram’s evaluation criteria [8]: (1) The surface of the restoration is smooth and without pitting. (2) There are no fractures or secondary caries. (3) There is no obvious discolouration of the restoration that compromises the aesthetics (Fig. 3). Meeting the above three conditions was considered to indicate clinical success.

Fig. 3.Frontal view at 12 months after RSC restoration. The restorations of 52–61 remained intact, with a smooth surface and good colour.

2.4 Statistical analysis

SPSS software version 20.0 (SPSS Inc., an IBM Company, Chicago, IL, USA) was used for the statistical analysis of all the data. The chi-square test was used to determine the success rate of RSCs for different parameters. For variables with a p value less than 0.05 in a preliminary analysis, a logistic regression analysis model was used to identify factors associated with the survival of restorations. Dummy variables were used for age and dental position, and p < 0.05 was considered to indicate statistical significance.

4.1 Influence of arch type on the restoration

The restoration of primary mandibular incisors presents an even greater challenge than that associated with other teeth. These teeth are very small, and the pulp cavity is very close to the enamel layer, making it difficult to prepare for the restoration of these teeth without exposing the pulp [3]. Consequently, direct composite resin restoration of primary mandibular incisors is difficult.

In this study, we used RSCs designed for maxillary primary incisors and primary lateral incisors to restore the mandibular primary anterior. Surprisingly, we found that the retention rate of the RSCs placed on teeth in the lower jaw was greater than that of RSCs placed on teeth in the upper jaw.

RSCs are composite resin restorations. Research on RSCs is limited; accordingly, to obtain a suitable reference we searched the literature on composite resin restorations. Demarco et al. [15] reported that restorations in the maxilla are more prone to failure in anterior teeth than in mandibular teeth. This is most likely related to the important role of the upper front teeth in the aesthetic appearance of patients. Sande et al. [16] reported that restorations in the lower jaw generally showed a greater survival rate than those in the upper jaw. Patients may have more easily perceived imperfections in their upper teeth, resulting in more interventions. Moreover, restorations performed in the upper jaw are affected by different masticatory forces and increased incisal stress compared to those in the lower jaw, which may also affect the results. Ideally, variables linked to the patient, such as the Angle’s classification, the incisal relationship, bruxism, and dietary habits, should be evaluated [16].

In this study, the high survival of RSCs placed on mandibular teeth may also be associated with fewer caries on the surface of the lower jaw teeth. A study showed that the prevalence of caries was greater in maxillary anterior teeth than in mandibular anterior teeth [17]. However, further analysis is required to confirm this finding. This discovery is surprising because using RSCs to restore mandibular anterior teeth simplifies the operation and can result in an aesthetically pleasing appearance. Moreover, a higher success rate was achieved. Therefore, paediatric dentists are encouraged to consider RSCs to be an ideal choice for the restoration of the lower anterior teeth.

4.2 Influence of tooth position on the restoration

Few reports exist in the literature on the use of RSCs in primary canines and mandibular anterior teeth. In this study, we placed RSCs on primary canines. However, the survival of RSCs placed on canine teeth did not achieve ideal results, which may be correlated with the large bite force borne by that of primary canine teeth. It is possible that crowns specifically designed for deciduous canine teeth can achieve the best results. To address this problem, we designed an RSC for deciduous canines and obtained a patent (Patent No.: ZL 2017 3 0648427.7). However, the effect of this new RSC must be validated clinically. In terms of the reason for the lower survival rate of primary lateral incisors, we could not explain it. Therefore, further clinical trials are needed.

4.3 Influence of the number of carious surfaces on the restoration

For all variables, the number of carious surfaces significantly affected the number of restorations. The survival of teeth with 1–2 carious surfaces was far greater than that of teeth with 3–4 carious surfaces. This is consistent with the findings of Ram and Fuks et al. [9]. The carious surface of the tooth can be considered an adverse factor that affects the survival of RSCs. This may be associated with the effective adhesion area. The adhesion region may remain less efficient as the amount of caries on the tooth surface increases. The longevity of the crown is likely to be jeopardized if a considerable amount of tooth structure is missing, as the composite crown relies on dentin and enamel adhesion for retention [18].

4.4 Influence of patient age on restoration

The results of this study revealed that the retention rate of RSCs placed on the teeth of older children was greater than that in younger children. Research has shown that older children (aged >3 years) have a lower risk of secondary caries than younger patients. This is naturally linked to difficulties in treating young children because of their limited ability to cooperate [19]. However, all children involved in this study underwent treatment under DGA; therefore, the children’s uncooperative behaviour had no effect on the treatment outcome.

The risk of caries is one of the most crucial factors affecting longevity. The longevity of restorations is challenged in patients at a greater risk of caries, as new carious lesions are likely to develop adjacent to restorations (secondary caries) [19]. One study showed that young children who underwent dental rehabilitation under DGA had poor oral health parameters and poor oral health-related behaviour [11].

In this study, the success rate was higher in the group aged >5 years than in the group aged 3–5 years, and the success rate was lowest in the group aged ≤3 years. We considered that the effect of patient age was likely linked to the greater risk of caries in these children. In addition, chewing habits may be another influencing factor, as older children have better compliance and are better able to follow medical advice to avoid biting hard objects with their front teeth, leading to a higher restoration survival rate.

4.5 Bonding problems

Generally, RSCs are bonded using an etch-and-rinse system. Selective enamel etching before the use of self-etching adhesives is highly recommended [20]. Another study demonstrated that one-step self-etching is inferior to multistep strategies for bonding to primary enamel [21]. However, a systematic review of the application of bonding to primary teeth reported that a mild universal adhesive system could substitute for etch-and-rinse and self-etch systems for restoring primary teeth [22]. In addition, Dijken et al. [23] reported no significant differences in durability between self-etch and etch-and-rinse adhesives. Another study revealed that after a one-year period, the self-etch adhesives tested presented clinical efficacy similar to that of the etch-and-rinse adhesive in restoring class II cavities in primary molars [24]. Furthermore, is it necessary to use a complete adhesive etching system for strip crown restoration? The rinsing of the acid etching causes discomfort and panic in children. In addition, it is crucial to reduce the operation time of DGA because prolonged surgery carries a greater risk of complications than what would normally be expected [25]. In paediatric dentistry, there is also a great need to shorten the application time. Reducing the number of clinical application steps can shorten the chair side time, providing additional advantages for treating young patients [26, 27]. This has motivated the use of self-etching adhesive systems and universal adhesives to bond enamel and dentin [20].

In this study, we used a universal adhesive system instead of selective enamel etching during the restoration procedure, and satisfactory results were obtained. However, research on which bonding system is most suitable for RSCs is limited. More clinical trials are necessary to compare the efficacy of universal and etch-and-rinse systems for RSCs placed on primary teeth.

4.6 Comparison of PVSSCs, ZCs and RSCs

The three full-coverage crowns for primary anterior teeth have their own advantages and disadvantages. RSCs have the benefits of multiple shade selections, the ability to fit crowded dentitions, and ease of repair [28]. However, RSCs are technique sensitive and difficulty controlling haemorrhages and saliva can occur during the restoration procedure [29]. Compared with PVSSCs, RSCs require longer clinical operation times and have shorter longevity [30, 31]. The disadvantage of PVSSCs is the adaptability of the crown to the tooth due to limited crimping, contouring, or squeezing of the crown. Moreover, the long-term retention and fracture resistance of the veneer are relatively low. Furthermore, PVSSCs are 5–8 times more expensive than RSCs [30].

The advantages of ZCs include colour stability, resistance to fracture or, good biocompatibility and autoclaving. The disadvantages are that the colour and shape are limited, the colour choices are more basic, and the shape cannot be adjusted. Consequently, more dental tissue must be removed to place a suitable dental crown [32]. As a result, ZCs can cause more dental tissue loss in teeth [33]. Finally, ZCs are more expensive than RSCs [34].

In summary, compared to PVSSCs and ZCs, RSCs have greater technical sensitivity and lower retention rates. On the other hand, RSCs require a smaller amount of tooth preparation; accordingly, more tooth tissue is preserved. Moreover, RSCs are less expensive.

Therefore, it is recommended that RSCs be chosen for vital teeth or patients with poor economic conditions. Due to the high technical sensitivity and the requirement for cooperation among children, RSCs are more suitable for older children, mandibular anterior teeth, central incisors, and teeth with fewer caries.

Notably, because data were collected from 2013 to 2016 there may be concerns about the timeliness and relevance of the findings in the context of current practices or advancements in the field. Although these data are not up-to-date, it is worth noting that over time, RSC restoration of primary anterior teeth has remained relatively stable and is still used today. In addition, the references cited in the study are new, providing a relatively new body of evidence for further validation research. Owing to older but relevant data and existing literature, we can understand this theme and highlight the objective value of this study better.