A Retrospective Study on the Fracture Toughness of the Coronal Restorations in Endodontically Restored Teeth. An Original Research

ABSTRACT

Introduction:

The best treatment for the deeply carious tooth that cannot be restored is by the root canal therapy. This method has saved many patients from the loss of tooth. The common practice is either to deliver a full crown or close the access cavity with restoration. Hence in this study, the clinical longevity of the routine practice is tested for by analyzing the fracture toughness and the survival of the teeth that were restored endodontically with various materials.

Materials and Methods:

The hospital records were retrospectively evaluated from 2000 to 2010 for a decade. The demographics as well as the survival and the failure rates noted and compared for the various types of the restorations. The number of the walls of the teeth was also compared.

Results:

Thousand teeth were considered in the study. Less than 7% of teeth had coronal fractures. Of the 93% teeth that had survived, the most common restoration was Individual post (+ crown) followed by GIC, amalgams, and crowns. The mean survival of the crown+ bridge & gold restoration was highest. The mean survival was 10 ± 2 years for the restored teeth without any fractures at the coronal level. The failure was greatest for the GIC followed by amalgam, and the variations when compared with other restorations were significant. There was no significant difference for the number of the walls on the crown; however, the number of walls present was proportional to the survival rate.

Conclusion:

The teeth that were covered with a crown were comparatively fracture resistant and had a better survival rate compared to other restorations. GIC showed highest fracture, and the post core with crown had the best survival. Restoration of the lost crown architecture and the reinforcement are the best methods that can be followed for the survivals.

INTRODUCTION

The treatment of the deep carious teeth as well as in few cases with the full mouth rehabilitation is by root canal treatment and coverage with crowns. The survival rates of these teeth have been studied previously. However, the studies that have discussed about the root canal restoration were usually compared between one or two restoration. The survival observed was an average of 9 years.[1-5] There are many factors that influence the survival of the teeth including the caries type, number of the walls that are sound, the efficiency of the dentist, the material used for the restoration, etc. Failure in either the steps of the root canal or the restorative phase may lead to the failure of the teeth. The structural reinforcement with the crown for an endodontic prevents the already damaged coronal portion against the masticatory forces. Endodontically treated teeth have a reputation for being fragile, which has been linked to fracture-causing fractures. The main cause of weakening endodontically treated teeth is now thought to be dental structural loss linked with restorative procedures (such as cavity and/or access cavity preparation), not desiccation.[6-10] Recent research has demonstrated that creating an endodontic access cavity only has a 5% effect on the relative cuspal stiffness of premolar teeth, as opposed to creating an occlusal cavity (20%) or a mesial-occlusal-distal (MOD) cavity (63% reduction).[8] In vitro, teeth were intact cracked under an average load of 345 kg, while teeth that had access cavities and MOD cavities fractured under loads of 222 kg, 222 kg, and just 122 kg, respectively.[9] This weakness was not corrected by a sealer and gutta-percha root canal filling.[10] Hard tissue fracture has been identified as the primary cause of endodontically treated teeth extraction in 41%–59% of instances.[11,12] Fuss et al.[13] research revealed that 10.9% of vertical root fractures and 43.5% of restoration failures in endodontically treated teeth necessitated extraction. Only 21.1% of the teeth were removed due to endodontic treatment failure. The authors came to the conclusion that if an adequate repair had been offered, more than 50% of the tooth removal may have been avoided.[14,15] To the best of our knowledge, however, there are currently very few clinical investigations on the single impact of the restoration after the root canal therapy on the survival of teeth. Hence in this study, the clinical longevity of the routine practice is tested by analyzing the fracture rate as well as the survival of the teeth that were restored endodontically with various materials.

MATERIAL AND METHODS

After the ethics approval was taken, the current retrospective analysis was undertaken. The hospital records from a designated tertiary care center were collected. The study period was set as between 2000 and 2010. For all these 10 years, the records of all the patients that had their permanent teeth restored after a root canal were analyzed. The various types of the restorations like the cements as well as the prosthodontic full crown restorations were included for the study. The composite filler material was used to close the access cavities using glue. All procedures were carried out by dentists on staff or first-year students at the School of Dental Science. The School of Dental Science constantly treated patients’ teeth, which was one of the inclusion criteria for the current study.

• Complete records of all procedures and examinations were kept.

• Following completion of endodontic care from the School of Dental Science, the patients took part in the recall system.

• To prevent tooth clustering within patients, the study only included one restoration per patient.

• A minimum of five years were considered for all the teeth to be included in the study.

• The opposing dentition and at least one approximate contact were present on the tooth.

The demographics were considered for the study as well as the period elapsed from the restoration, type of restoration, failure, and reasons. The fractured teeth and the reason were keenly noted as well as the restoration during that time was noted. The RCT-treated teeth along with the restoration that were fractured were considered in this study. The other fractured teeth that were not restored endodontically were excluded. A final of thousand teeth were included that fit the selection criteria and hence were subjected to the analysis.

Analytical statistics

All variables underwent descriptive analysis that included mean and standard deviation. The observations were represented as frequencies and percentages. These values were analyzed using the Chi-square test. For the descriptive analysis, the central tendency and dispersion indices were displayed using the relevant charts and tables. Using SPSS 23, the P < 0.05 was taken as significant.

RESULTS

The total number of the teeth that were considered in the study was 1000. The mean age of the subjects was 57 ± 1 year. The male-to-female ratio observed was 1.7:1. There was a slight male predilection; however, the variation seen was not significant. The restorations that were observed in the study were glass ionomer, composite, amalgam and full ceramic, or metal ceramic and gold crowns. The highest percentage of the restorations in this study was with the Individual post (+ crown) followed by GIC, amalgams, and crowns. The mean survival of the crown + bridge & gold restoration was highest. The mean survival was 10 ± 2 years for the restored teeth without any fractures at the coronal level. The number of the walls observed in this study was distributed as 1 & 2 walls and 3 & more walls. It was observed that 1 & 2 walls survived better than 3 or more walls. The number of walls in the present study was almost evenly distributed in the present study as shown in Table 1.

Table 1.

Distribution and the survival of the included restorations

Restoration	Percentage distribution	Survival	Means	SD
Amalgam	15%	71%	11 years	±3
Composite	6%	92%	10 years	±3
Crown/bridge	10%	96%	10 years	±2
Crown/bridge with access cavity	8%	97%	11 years	±3
Glass ionomer cement	15%	64%	10 years	±2
Gold partial crown	4%	100%	9 years	±2
Individual post (+ crown)	37%	96%	10 years	±2
Prefabricated metal post (+ crown)	10%	86%	10 years	±2
Total	100%	87%	10 years	±2
Surface	-	-
1 & 2	-	-	12	2
3 & more	-	-	11	2

The total number of the teeth that were finally analyzed for the study was 927. When compared with the other restorations, the GIC had least survival. This variation was significant. All the other restorations were almost similar in fracture resistance and had a similar survival rates. The second least survival rate was seen for the amalgam. Table 2 shows the survival rates and the comparison of restorations among each other.

Table 2.

Comparison of the survival of the included restorations

Restoration	Survival	GIC	Amalgam	Prefabricated	Composite	Crown/bridge	Individual post + crown	Crown/bridge with access cavity	Partial crown
GIC	7±1 years		0.000*	0.000*	0.000*	0.000*	0.000*	0.000*	0.000*
Amalgam	12±1 years	0.001*		NS	0.000*	0.000*	0.000*	0.000*	0.000*
Prefabricated metal post + crown	13±1 years	0.000*	NS		NS	0.000*	NS	NS	NS
Composite	14±1 years	0.000*	NS	NS		NS	NS	NS	NS
Crown/bridge	15±1 years	0.000*	NS	NS	NS		NS	NS	NS
Individual post + crown	14±1 years	0.000*	0.000*	NS	NS	NS		NS	NS
Crown/bridge with access cavity	16±1 years	0.000*	NS	NS	NS	NS	NS		NS
Partial crown		0.000*	NS	NS	NS	NS	NS	NS

DISCUSSION

The study’s aim was to find if the restoration that is given after the endodontic treatment influences the survival of the treated tooth. This study was one of the firsts that has evaluated a decade-long retrospective record and has considered the effect of the restoration on the tooth survival. A major benefit of retrospective observational studies is that a lot of cases and data may be evaluated. Although this type of study methodology is observational, it offers a straightforward “picture” of a participant group at a certain point in time. Because the data that can be analyzed are constrained by the information that is now accessible and hence prone to interpretation biases, it can be considered a known limitation in this study. The endodontic issues such persistent pain, swelling, or sinus tract can lead to tooth extractions, but similar issues could also be caused by coronal leaking from a flawed coronal restoration. On the other side, an unidentified root fracture may be connected to a deep periodontal probing deficiency. However, the results of the current study may help in making decisions for the choice of the restoration after the root canal. The current research, however, solely examined how often teeth fracture in connection to the restoration that was given.

According to the current study, 10 ± 2 years of average survival period were evidenced. The survival percentage is 92.7% of teeth with post-endodontic restorations remaining intact. According to statistics, the average survival was 14 years. This proved the fantastic long-term prognosis of teeth with post-endodontic restorations. The patients’ gender had no bearing on the outcomes.[15] The age was not correlated in the study; however, it was observed that the maximum number of the subjects who had a coronal fracture was over 40 years of age. This may have been due to lost tooth structure to extensive cares or tooth attrition. This was also shown in some previous studies.[16-20] Additionally, there was no discernible difference between teeth that were premolars or molars and those that were in the upper or lower arch, respectively. Therefore, the outcome of fractures was unaffected by the patient’s age or the type of tooth. However, the fracture resistance was significantly impacted by the choice of the restorative material.

The finding shows that the maximum percentage of the restoration was with GIC. This was contrary to the general perception that will point to the full coverage crowns. However, GIC only worked as a temporary filling in all of these teeth because this cement enables the clinician to fill the cavity when the root canal filling is complete without the need for any additional pretreatment.[18] Why so many teeth were not given a permanent repair following successful root canal therapy is still a mystery. The patients may have been reluctant or less motivated to attend for the final restoration since GIC was effective. Corroborating to this, the present study’s findings show that the highest fracture rate was with the GIC. Other researchers discovered a 34.5% survival rate for temporary restorations over a 3.17-year observation period, showing that these restorations have a much lower survival rate than permanent replacement materials.[17] However, as this was not a randomized experiment, conclusions about whether or not GIC should be utilized are improper. For instance, it is also possible that the operator chose GIC because they thought the prognosis may be poor or for another factor that has to do with the survival of the tooth. After GIC, amalgam-restored teeth had the second-highest mean breakage rates. The GIC and amalgam groups had the worst outcomes as a result of the materials’ inability to stabilize the tooth and shield it from breakage. Additionally, undercuts are necessary for cavities that will be filled with amalgam, which could further compromise the tooth’s structure.[8,19-21]

For teeth with composite fillings, the average lifespan was 14 years. Despite the fact that composite fillings have a greater rate of survival than amalgam or GIC fillings, this difference was statistically insignificant. Less than 6% of the present study’s subjects were treated with the composite. In general, teeth filled with adhesive composites outperformed teeth filled with amalgam in terms of fracture resistance.[19,22,23] Today, composites are regarded as the best restorations immediately following RCT because of this significantly greater stability of the root canal-treated tooth and bacteriostatic nature.[15]

In earlier research, crowned teeth fared better in terms of survival than teeth with alternative restorations.[11,24] In the current study, complete crowns had a considerably lesser mean breakage rate than teeth replaced with GIC or amalgam. There was no difference in individual crowns alone and the treated with the post and the crown in this study. While Willershausen discovered that teeth repaired with posts and crowns had much worse survival rates than teeth treated merely with a crown, this conclusion is in agreement with previous recent publications.[25-27] The root is further weakened as a result of the root canal’s preparation for post-insertion, which eventually affects the entire tooth.[8,9,27-31] When feasible, avoid using metal posts since they weaken teeth that have had root canal therapy.[32] No posts or cores are required if there is enough enamel and dentin to guarantee the correct retention of a typical crown repair.[8,9,27-31]

The posts with screw threads placed more stresses on the tooth structure and should thus be avoided because they run the risk of fracturing.[34] In general, it must be taken into account that teeth restored with posts had more dental structure lost prior to the RCT than other teeth, which may affect the teeth’s fracture resistance. Due to their modest sample size (n = 24), all of the gold partial crowns in the current study survived the observation period. It could be demonstrated that, in comparison to the intact tooth, a cast gold onlay increased the relative fracture resistance.[19] It seems that simply covering all of the cusps is enough to stabilize a tooth that has undergone endodontic treatment.[14,21]

Compared to teeth with three or more areas of decay, teeth with up to two surfaces of decay fared much better. After restoration with filling materials, it was discovered that severe crown loss increased the fracture percentage.[15] Numerous in vitro research have supported this clinical conclusion.[9,14,19,3-35]

The limitations of this study other than being retrospective were that the correlation between the demographics and the fracture was not addressed. There was a wide disparity of the age between the subjects. The cause of the trauma was absent for few study participants.

CONCLUSION

Comparing the fracture rates of whole crowns with access cavities that were adhesively sealed to post-endodontically supplied crown restorations. When compared to full-coverage crowns, gold partial crowns fracture at a rate similar to that of full-coverage crowns. With composite filling material, less damaged crown structure can be well restored. Additional research is needed to determine the fracture rates of emerging endodontic treatment approaches.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.