Restoration of Root Filled Teeth; Current Opinions and Techniques

1. INTRODUCTION

Root canal treatments are normally indicated when pulpal health has been jeopardized beyond repair and removal of the pulp tissue is needed. The primary goals of endodontic treatment are to relieve pain or discomfort, clear or prevent infection, and to restore normal occlusion, function and aesthetics [1]. Usually Root Filled Teeth (RFT) suffer from substantial loss of coronal tooth structure resulting from the presence of primary or secondary caries, restorations, trauma and access cavity preparation [2]. There are also changes in the structural and mechanical properties of dentine that occur following endodontic treatment [3, 4] and the accompanying loss of coronal tooth structure [5]. Hence the prognosis of the RFT is highly dependent on the design of the final restoration [6, 7].

With improvements in bonding to tooth structures, RFT can be restored with direct resin composites or indirect restorations when cuspal coverage is deemed necessary. Endocrowns and partial crowns have also been suggested recently to restore RFT with extensive loss of coronal tooth structure [8, 9]. Nevertheless, intraradicular posts may be deemed necessary to improve retention of the restoration material to the remaining tooth structures particularly when incomplete ferrule is established. A wide range of posts and cement types are available on the market for restoring endodontically treated teeth.

Previous studies have shown that the prognosis of RFT depends not only on the remaining tooth dentine [10] but also on the periapical status and position of the tooth, the number of adjacent teeth and occlusal contacts [11]. It is further influenced by post-endodontic restoration [12]. This will leave the restoring dentist with decisions to contemplate to use a post or not, which post, how to prepare the post space, which cement, and many other aspects [13].

Several types of intraradicular posts are available, including cast metal post and prefabricated post [10, 14-17]. Glass fiber posts are currently the most popular [18]. Compared with metal post, glass fiber post has the following advantages, such as better aesthetics, similar modulus of elasticity and rigidity comparable to dentine. Glass fiber posts have a lower risk of root fracture than metal posts [19].On the other hand, glass fiber post normally fails due to loss of retention [20].

A wide range of restorative materials can be used as a core material or direct restorations such as composites, amalgam, glass ionomer and resin-modified glass ionomer [21]. The indirect restorative options could be ceramics, metal ceramics, gold alloys and base metal alloys, which can be produced using conventional techniques or CAD/CAM technologies [22].

Dentist-related factors like experience and postgraduate training can influence the decision-making process [23]. The skills of a dentist can be improved over time in clinical practice. However, the introduction of new materials in the market requires training and updating knowledge of dentists to ensure the best applications of the new materials [23-28].

Inadequate restorations adversely affect the prognosis of the tooth regardless of the quality of the endodontic treatment [6]. Despite the large amount of literature relative to the restoration of the RFT, dentists appear to slowly adapt to new knowledge and technologies. Lack of awareness among dentists regarding modern concepts and techniques could compromise the quality of dental care, especially in developing countries where financial resources might be limited.

The number of qualified dentists per capita in Jordan is probably one of the highest in the Middle East. Although a small percentage of dentists enroll in advanced education or training in restorative dentistry or prosthodontics, most practicing dentists lack further formal education beyond their basic dental degree. In addition, more than half of general practitioners obtain their educational qualifications from various schools worldwide; therefore, considerable variations in education background and clinical experiences exist among Jordanian dentists.

Surveys are an important tool for discerning dentists’ understanding of treatment attitudes and their knowledge about RFT which is gained by sharing experience between practitioners [29].

National and multinational surveys regarding the restoration of RFT have been carried out in many countries, including the USA, Northern Ireland, Sweden, Switzerland, Saudi Arabia, Germany, Brazil, India and New Zealand [29-37]. No research of this kind has been carried out in Jordan. The purpose of this study is to investigate the current concepts, opinions, techniques and materials used among dentists practicing in Jordan with regard to the restoration of RFT.

2. MATERIALS AND METHODS

This research project was approved by the ethics committee of the school of dentistry, the University of Jordan(201/2019), and carried out between June and September 2019. The required information was collected through an anonymous questionnaire. The questionnaire was adopted from a previous study [37] and modified to suit the requirement of the present study. Dentists who gave their consent to participate could access and complete the questionnaire via the online link. All responses were anonymous.

The questionnaire was first piloted among 10 specialist dentists and 20 general dental practitioners. Feedback was sought regarding the completeness and clarity of the questions and the questionnaire was amended accordingly. The final format of the questionnaire consisted of two parts, demographic information and multiple choice type questions. The demographic part of the questionnaire consisted of six questions regarding dentists’ personal information; age, gender, highest qualification, country of the professional dental degree, workplace and experience.

The second part contained 24 questions focused on the treatment opinions of post-endodontic restoration, materials and techniques used. The dentist was permitted to choose more than one answer in 6 out of 24 questions. The questions covered the following topics:

3. RESULTS

3.2. Beliefs and Frequency of Use of Posts

Of the GDPs, 37.8% restored more than 20 RFT per month compared to 29.8% and 52.9% of the prosthodontists and endodontists, respectively.

A significantly higher percentage of GDPs believe that RFTs are more susceptible to fracture compared to teeth with vital pulps compared to prosthodontists and endodontists (P = 0.002). The gender of respondents or their length of experience or country of graduation did not affect this belief; however, significantly less percentage of respondents practicing at universities held that belief (P= 0.001). Although a higher percentage of GDPs believed that every RFT must receive a post compared with prosthodontists and endodontists, the difference did not reach statistical significance (Table 2). The latter belief was significantly held by a higher percentage of those who practiced at the Ministry of Health (P= 0.043), had more than 15 years of clinical experience (P= 0.002), and those who graduated from other Arab countries or Asian countries (P= 0.024).

As shown in Table 2, prosthodontists and endodontists believed that the main advantage of posts is to provide retention to the core material, while GDPs believed that posts reinforce RFT and provide retention to core material (P<0.001) Table 2. The belief that posts reinforce RFT was held by a higher percentage of males (P= 0.022), those who graduated from other Arab or Asian countries (P<0.001), those who practiced at Ministry of Health and private clinics (P= 0.002), and those who had more than 15 years of clinical experience (P<0.001). Significantly more GDPs believe that pins should be used instead of a post for the retention of a core material (P = 0.002).

Table 1.

-		General practitioners %	Prosthodontists %	Endodontists %
Clinical practice	Ministry of Health	87.5	7.8	4.7
	Royal Medical Services	63	30.5	6.5
	Private	81.4	13.6	5
	University-based	46.2	38.8	15
Country of professional degree	Jordan	77.9	16.2	5.9
	Other Arab countries	85.1	8	6.9
	Asian countries	86	11.6	2.3
	West Europe & USA	31.4	54.9	13.7

Table 2.

Question	Response	General practitioners %	Prosthodontists %	Endodontists %	P-value
Do you believe that RFT are more susceptible to fracture compared to teeth with vital pulps?	Yes	93.8	83	85.3	0.002
Do you believe that every RFT must receive a post?	Yes	5.5	1.1	0	0.072
Do you believe that a post will reinforce an RFT and reduce the chances of fracture and/or provide retention for the core material?	Reinforce	7.3	3.2	2.9	<0.001
	Provide retention	48.8	78.7	79.4
	Both	37.5	13.8	11.8
	None	6.3	4.3	5.9
Do you believe that pins should be used instead of a post for the retention of a core material?	Yes	12.3	2.1	0	0.002

When asked when should an RFT receive a final restoration, the majority of respondents (77.1%) believed that RFT should receive a final restoration as soon as possible after endodontic therapy (Fig. 1). Significantly, a higher percentage of GDPs (P= 0.004), graduates of Asian countries (P<0.001), and who had more than 15 years of experience (P=0.001) believed that RFT should receive a final restoration at least one month after obturation.

As shown in Fig. (2), respondents thought that satisfactory root canal filling is the most important factor that should be evaluated on a radiograph before canal preparation for a post. This belief was not affected by gender, place of practice, country of graduation, experience, or qualification of respondents.

When asked about the minimum vertical tooth structure required to provide an adequate “ferrule effect”, 64.2%, 23.5%, and 5.7% of respondents thought that it should be 2mm, 1mm, 0.5mm, respectively, while the rest thought that it is not mandatory to have a ferrule. This belief was not affected by gender, place of practice, country of graduation, experience, or qualification of respondents.

As shown in Fig. (3), respondents thought that the length of the post is the most important factor to ensure the successful retention of a post. However, respondents working at the Ministry of Health (51.6%), and the graduates of Asian countries reported that the thread design of the post is the single most important factor post retention.

3.5. Pre-treatment and Cementation of Posts

Nearly three-quarters of practitioners reported that they treat the prepared post hole before cementing the fiber post (Table 5). The two most common rinsing solutions were phosphoric acid and sodium hypochlorite. Sodium hypochlorite was used less frequently by graduates from the West Europe and USA, more frequently by those who had more than 15 years of clinical experience and it was the most common rinsing solution for those working at MH.

Table 5.

Question	Response	%	Gender	Qualification	Country of graduation	Practice location	Experience
			P-value
Preferred cement for metal posts	Zinc phosphate cement	14.8	NS	0.04	0.03	NS	NS
	Polycarboxylate cement	9
	Glass Ionomer cement	49.1
	Resin-modified glass ionomer	14.2
	Adhesive resin cement	12.9
Preferred cementation technique for fiber posts	Acid etch/rinse and dual cure resin	37.7	NS	<0.001	0.007	<0.001	NS
	Acid etch/rinse and light cure resin	11.7
	Self-etching/self-adhesive dual cure resin	28.9
	Self-etching/self-adhesive light cure resin	5.5
	Resin modified Glass Ionomer	6.9
	Glass Ionomer	9.2
Pre-treatment of radicular dentine (prepared post hole) before cementation of fiber post	Alcohol immersion	6.4	NS	NS	0.01	0.001	0.046
	Chlorohexidine immersion	5.3
	Sodium hypochlorite	12.3
	Phosphoric acid rinsing	36.9
	EDTA	5.5
	Phosphoric acid rinsing and EDTA	10.0
	No pre-treatment	23.6
Surface treatment of fiber post before cementation	Air abrasion	5.4	NS	<0.001	0.025	NS	NS
	Silane application	14.8
	Air abrasion/Silane application	11.0
	Adhesive (dentine bonding agent) application	23.9
	No pre-treatment	44.9

More than half (55.1%) of respondents reported that they surface treat fiber posts before cementation. The most common surface treatment was applying an adhesive dentine bonding agent and the second most common treatment was silane application. However, silane application was the most common approach used by endodontists, while it was the least common approach used by graduates from Asian countries.

Most practitioners use glass ionomer cement for luting a metal post, followed by zinc phosphate (Table 5). However, the second choice of cement by GDPs was silver-modified glass ionomer and adhesive resin cement was chosen by graduates from other Arab countries. In the case of fiber posts, the most common technique used by respondents was acid etch/rinse and dual cure resin, followed by self-etching/self-adhesive dual cure resin. However, prosthodontists and endodontists, graduates from Asian countries, and those working at dental schools preferred more self-etching/self-adhesive dual cure resin as their first choice cementation technique.

4. DISCUSSION

This study aimed to investigate the current opinions and practices of Jordanian dentists when restoring RFT. The response rate (62%) was comparable to similar studies [36, 38] and well above the response rate of two recent surveys regarding the impact of Covid-19 on dental practices in Italy [39, 40]. Thus, the current survey could be considered representative of all Jordanian dental practitioners. Dentists restoring RFT with extensive loss of tooth structure are faced with a plethora of options regarding timing, materials preparation and conditioning techniques when placing definitive restoration after root canal treatment is successfully completed [41]. The majority of dentists who responded to this survey favored restoration of RFT as soon as possible or within less than one month. Providing definitive restoration in a short time span has been shown to yield favorable outcomes [42]. Immediate or within short time span definitive restoration of RFT was also chosen by dentists in Germany [32, 43] and Greece [44]. This might also explain why more endodontists tend to place more posts than both prosthodontists and GDPs.

New adhesive techniques have allowed a more conservative approach, including adhesive direct fillings, partial crowns and endocrowns [7, 45]. In this study, only a minority of dentists contemplated placing a direct restoration only when dealing with RFT with extensive loss of coronal tooth structure. Most dentists reported using a post and core followed by conventional full-coverage metal-ceramic or all-ceramic crowns. More dentists contemplated using endocrowns or onlays when restoring molars compared to premolars or anterior teeth. The presence of more coronal tooth structure available for bonding in molars might explain this trend.

In contrast to Prosthodontists and Endodontists, more GPDs in this study held the belief that restoring RFTs with posts would increase the fracture resistance of those teeth. While this cannot be supported by current evidence, this belief was also shared by more GDPs than restorative specialists in other countries as well [29, 32, 35, 38, 46].

Arguably one of the most important factors when considering favorable prognosis of root treated teeth is the presence of a “Ferrule” [47, 48]. The presence of at least 1.5-2mm of vertical tooth structure circumferentially has a positive effect on the fracture resistance of RFT [49]. This was chosen by almost two-thirds of dentists in this study and was also chosen by a majority of dentists in Sweden [29] and Germany [32].

When restoring RFT anterior teeth, the majority of dentists reported using fiber posts. Fiber posts were still the first choice in premolars and molars to lesser degrees, followed by prefabricated metal posts, while cast metal posts were the least popular to use in all three categories of teeth; anteriors, premolars and molars. Favoring prefabricated fiber and metal posts over cast posts may be attributed to the need for another extra clinical visit when using the latter. This trend was noted in a recent UK survey as well [50]. The popularity of fiber posts use was also reported in another multinational survey [35]. Cast posts tend to perform better when the ferrule is lacking or severely jeopardized [51]. Comparable performance was noted after 5 years of service between cast gold post and core and fiber post and composite core when adequate ferrule was present [52].

More than half of the dentists who regularly use prefabricated metal posts prefer to use active (threaded) posts. In literature, it has been shown that active threading would increase the likelihood of developing cracks inside radicular dentine, thus increasing the chances of root fracture [53]. It has been suggested that active threaded posts should be considered when roots are excessively short or bonding to radicular dentine is not predictable using fiber post or luting a smooth (passive) cast post does not provide enough retention [54, 55].

There was a general tendency to use more extracoronal indirect restoration for posterior RFT when compared to anterior RFT by dentists surveyed in this study. All-ceramic crowns were the preferred choice for anterior and premolar teeth. While dentists surveyed have used more metal-ceramic crowns on molar teeth, they also tended to use endocrowns with no post more in molars when compared to premolars.

When using RFT as bridge abutment, dentists surveyed in this study still favored fiber posts over cast or prefabricated metal post. The choice of material for final FPD was more toward all-ceramic when the RFT retainer was an anterior tooth, and toward metal-ceramic or all-ceramic material when the RFT was a premolar. When a molar RFT was used as an FPD retainer, more dentists preferred to use metal-ceramic material. The tendency to use metal-ceramic bridges in posterior teeth might be attributed to lower costs and easier maintenance. This tendency might also be attributed to the higher loss of porcelain material in veneered zirconia bridges [56].

The adequacy of root filling as evaluated in post obturation radiograph was the main factor that most dentists chose before preparing the canal space for a post. This was in line with European quality guidelines for endodontic treatments [57]. Poor technical quality was also the driving factor to consider retreatment for Jordanian dentists surveyed for the management of asymptomatic RFT with apical periodontitis [58]. A minority of dentists only chose the absence of clinical symptoms as the most important factor to consider when they are preparing canal space to receive a post.

Glass ionomer was the preferred cement to use with metal posts, followed by Zinc phosphate cement. Conventional dual cure resin cement with etch and rinse bonding strategy was predominantly used when bonding fiber posts followed by self-adhesive dual cure resin cement. Self-adhesive bonding strategy is less sensitive technique when compared to etch and rinse which might provide a leeway for the inexperienced dentists [18, 59]. It was found to be used more frequently than etch and rinse conventional cements by respondents in different countries [35]. Although Jordan is one of the courtiers who signed the Minamata convention to phase down amalgam by 2020 [60], this survey showed that 10-15% of respondents are still using amalgam regularly as a core build-up material.

Almost half of the dentists surveyed did not use any pretreatment to fiber posts before cementation, and only a minority of dentists would use an alcohol swap to clean posts before cementation. Interestingly, higher percentages of surveyed dentists use either phosphoric acid etch or sodium hypochlorite to condition posthole space. Sodium Hypochlorite used as the final irrigant was shown to adversely affect the bonding of post to radicular dentine [61-63].

As the majority of dentists surveyed in this study predominantly used fiber posts, the reasons of failure reported by them were mainly associated with fiber posts like loss of retention and fracture of coronal tooth structure. This was similar to the common failures associated with fiber post as reported in the literature [18].

CONCLUSION

It can be concluded that the selection of materials and techniques to restore RFT varies considerably between dentists in Jordan and is not necessarily evidence-based. Further training and continuous education courses might help reduce inconsistencies that have been noted while restoring those teeth.

REFERENCES