Incidence of restoration failure and its etiology: A retrospective study

Abstract

Context:

Restorative dentistry plays a critical role in maintaining oral health, function, and esthetics by repairing damaged or decayed teeth. Restoration failures can arise from several factors, such as material degradation, improper technique, patient-specific oral conditions.

Aim:

The present study aimed to evaluate the incidence of restoration failure among different permanent restorative materials and to analyze the causes of restoration failure.

Materials and Methods:

Four-hundred patients were examined for restoration failure over a time period of 19 months, reported at the outpatient section of the department of conservative dentistry and endodontics. A self-structured pro forma was designed, and each patient was given a code number. The details about the patient and causes of failure of permanent restorations were obtained by using a questionnaire which included information on patient’s oral hygiene habits and history of restoration placement.

Statistical Analysis:

Data obtained were statistically analyzed by the Chi-square test.

Result and Conclusion:

Statistically significant differences (P < 0.0001) were found in the case of age groups, reason of replacement, and the class of restoration. The main cause of the failure was secondary caries, followed by microleakage and bond failure. Composite was the most commonly replaced restorative material, and mandibular molar teeth showed maximum failures. It also indicated that replacements were more prevalent in males.

INTRODUCTION

Restorative dentistry aims to enhance the overall health, appearance, and functionality of teeth. It encompasses diagnosing, preventing, and treating both carious and noncarious lesions. The necessity for restorative dentistry arises when teeth exhibit cavities, damage, and breakage or are missing and when restorations become dislodged. It provides an optimal opportunity for sustained oral health and restores teeth to their full functionality and esthetics by addressing decay and damage.[1]

While selecting restorative materials, various factors come into consideration, with longevity typically taking precedence. According to Hofsteenge et al.,[2] the longevity of resin restorations after replacement of amalgam on molars and premolars for 15 years of observation period in 88 patients was 74.7%. Another study[3] observed the survival rate of 269 direct posterior amalgam restorations, and resin composite restorations in Class I and Class II were 8.7 years and 5.0 years, respectively.

Moreover, the replacement of restorations is more common than their initial placement in routine clinical practice. Studies[4,5] have reported a replacement-to-primary restoration ratio for composites (80:20) and for silver amalgam (70:30), with even greater ratios documented. Several factors influence this proportion, including the age group studied, with higher replacement rates observed in adolescents compared to adults and lower rates in deciduous teeth. In addition, a patient’s oral hygiene, awareness, and programs of caries prevention also contribute to this trend.[6]

The present study evaluated the incidence of restoration failure, and the reasons for replacing direct restorations were analyzed, correlating the replacements with patient-related, tooth-related, and restoration-related factors in permanent teeth. Furthermore, the longevity and survival rate of different restorative materials used in dentistry.

MATERIALS AND METHODS

The present study was done on individuals reporting at the outpatient section of the department of conservative dentistry and endodontics, at a dental institute. This was carried out for a period of 19 months (February 2023–September 2024). Examination of the patients was done after isolation of the teeth. A self-structured pro forma [Table 1] was designed, and each patient was given a code number. The information about the patient and causes of failure of permanent restorations were obtained. A pro forma was utilized to collect data on the patient’s oral hygiene practices and restoration placement history, and written informed consents were obtained.

Table 1.

PERFORMA including causes of restoration failure

Serial number/date of examination OPD number Age/sex Mobile umber Tooth number
Factors responsible for failure of restoration
A. Restorative causes	B. Endodontic causes	C. Periodontal causes	D. Orthodontic causes	E. Clinician related	F. Miscellaneous	G. Probable causes
1. Site of fracture/failure (MOD) Mesial Distal Occlusal	1. Site of fracture/failure (MOD) Mesial Distal Occlusal	1. Oral hygiene Fair - f Poor - p	1. Parafunctional habits (0, 1)	1. Experience (months)	1. Deleterious habits (0, 1)	1. Microleakage 2. Bond failure 3. Restoration fatigue 4. Improper tooth prep 5. Improper proximal contact 6. Insufficient tooth structure 7. Crown not present
2. Restorative material Amalgam - A GIC - G Composite - C	2. Restorative material Amalgam – A GIC - G Composite - C	2. Brushing frequency (1, 2)	2. Occlusion Angle’s class I, II, III
3. Type of tooth preparation Class I, II, III, IV, V, VI	3. Type of access cavity preparation Class I, II	3. Type of brush Soft - 1 Medium - 2 Hard- 3	3. Overjet (mm)
4. Longevity (months)	4. Longevity (months)	4. Type of paste Fluoridated - 1 Nonfluoridated - 2	4. Overbite (mm)
5. Secondary caries (+, −)	5. Secondary caries (+, −)

MOD: Mesial–occlusal–distal, GIC: Glass-ionomer cement

Sample size calculation

To obtain a representative sample size, the Raosoft formula was used. As the total number of samples available for the study was determined based on the inclusion criteria, and the population size was unknown, a response distribution of 50% was assumed for a large population. Therefore, the minimum required sample size was calculated to be 277. Considering several relevant factors, the sample size for the study was increased to 400.

Study setting

A retrospective study analyzing the records of placed restorations was conducted to identify the causes for their replacement. The direct examination involved a visual assessment using a standard mouth mirror and a sharp-ended explorer (API Germany Stainless CE 10-16: Probe D/E), an intraoral camera (Waldent Intraoral Camera USB Model), and intraoral photographic mirrors (Capri Photographic Mirrors) [Figure 1]. Selection was carried out according to the specific inclusion and exclusion criteria.

Figure 1.

Intraoral images of restorations captured through an intraoral camera and radiograph

Inclusion criteria

• Dislodged restorations

• Restorations requiring replacement due to discomfort

• Age >16 years.

Exclusion criteria

• Teeth without any prior restorative intervention

• Patients who do not present with restorations requiring replacement

• No teeth with cracks, fractures, or structural defects

• No teeth with developmental anomalies.

Questionnaire

For each case, the following details were recorded: the code number, gender (male or female), and age group categorized as 16–30 years, 31–45 years, 46–60 years, and above 60 years. Data on the frequency of brushing per day were also noted. The reason for restoration replacement was identified as either fracture or recurrent caries. The restorative material used was documented as amalgam (A), composite (C), or glass ionomer cement (GIC) (G). The class of tooth preparation was recorded as Class I, II, III, IV, V, or VI. The site involved was specified as maxillary or mandibular, and further as right or left side. The tooth involved was classified as incisor (A), canine (B), premolar (C), or molar (D). Information regarding oral hygiene measures and occlusion type, based on Angle’s classification (Class I, II, or III), was also included. Additionally, the experience of the operating dentist was recorded as less than 36 months (learner) or more than 36 months (experienced).

The reasons for restoration failure were documented, and since the records were self-explanatory, multiple reasons could sometimes be identified for a single case. The collected data were statistically analyzed using the Chi-square test.

RESULTS

In this study of 400 patients, restoration failures were highest in the 31–45 years of age group (40.5%) and lowest in >60 years (6.0%) [Table 2, P = 0.0001]. Younger patients (31–45 years) showed the most failures, but this could partly be due to dietary habits, stress-related bruxism, or higher caries incidence in this age group, not just material or cavity class. Gender-wise, males (52.0%) showed slightly more failures than females (48.0%), but this was statistically nonsignificant (P = 0.427). Tooth distribution showed maximum failures in 36 (17.8%) and 46 (12.8%), with Class II preparations having the highest failure rate (67.75%) and Class IV the least (1.25%) [Table 2, P = 0.0001]. Restorative causes (71.5%) predominated over endodontic causes (28.5%) [Table 2, P = 0.0001]. Among materials, composites accounted for the majority of failures (69.5%), followed by amalgam (24.25%) and glass-ionomer cement (GIC) (6.25%) [Table 2, P = 0.0001].

Table 2.

Association of demographic and clinical factors with restoration replacement

Category	Incidence (%)	P
Age group (years)
16–30	108 (27.00)	0.0001
31–45	162 (40.50)
46–60	106 (26.50)
>60	24 (6.00)
Total	400 (100.0)
Gender
Males	208 (52.0)	0.427
Females	192 (48.0)
Total	400 (100.0)
Teeth
16	35 (8.8)	0.0001
26	38 (9.5)
36	71 (17.8)
46	51 (12.8)
Class
I	106 (26.50)	0.0001
II	271 (67.75)
III	5 (1.25)
IV	9 (2.25)
V	9 (2.25)
Total	400 (100.00)

Site-wise, occlusal failures were most common (51.25% in restorative and 23.0% in endodontic), followed by distal and mesial sites; secondary caries was present in 73.5% of dislodged restorations [Table 3, P = 0.0001]. Composite showed the highest association with secondary caries (50%), followed by amalgam (18.5%) and GIC (5.0%) [Table 3, P = 0.0001]. Up to 36 months, composite demonstrated the highest failure rates in both restored teeth (45.1%) and endodontically treated teeth (ETT) (68.42%), while amalgam showed greater longevity beyond 36 months [Table 3, P = 0.0001]. Patients in the composite group were younger on average compared to those receiving amalgam, suggesting that age could act as a potential confounding factor in material-related failure rates. Operator experience (<36 vs. >36 months) did not significantly influence failure rates [Table 3, P > 0.05].

Table 3.

Association between material, cause, and site of failure for restoration replacement

		Incidence (%)			P
Category
Restorative (R)		286 (71.50)			0.0001
Endodontic (E)		114 (28.50)
Total		400 (100.0)
Material used
Amalgam (A)		97 (24.25)			0.0001
GIC (G)		25 (6.25)
Composite (C)		278 (69.50)
Total		400 (100.00)
	Restorative causes, incidence (%)			Endodontic causes, incidence (%)	P
Fracture site
Mesial (M)		63 (15.75)		36 (9.00)	0.0001
Distal (D)		97 (24.25)		67 (16.75)
Occlusal (O)		205 (51.25)		92 (23.00)
Secondary caries
Absent (−)		106		26.50	0.0001
Present (+)		294		73.50
Total		400		100.00
	Amalgam, frequency (%)	GIC, frequency (%)	Composite, frequency (%)	Total, frequency (%)	P
Longevity (months)
Up to 36 months	25 (8.74)	14 (4.90)	129 (45.10)	168 (58.74)	0.0001
>36 months	58 (20.28)	4 (1.40)	56 (19.58)	118 (41.26)
Total	83 (29.02)	18 (6.29)	185 (64.69)	286 (100.0)
Longevity (months)
Up to 36 months	8 (7.02)	4 (3.51)	78 (68.42)	90 (78.95)	0.123
>36 months	6 (5.26)	3 (2.63)	15 (13.16)	24 (21.05)
Total	14 (12.28)	7 (6.14)	93 (81.58)	114 (100.0

GIC: Glass-ionomer cement

Analysis of probable causes [Table 4] revealed microleakage (99.25%), bond failure (69.75%), improper contacts (24.0%), and faulty preparation (14.5%) as major reasons in vital teeth. In ETT, absence of crowns (25.5%) and insufficient tooth structure (11.75%) were the leading causes (P = 0.0001).

Table 4.

Association between the experience of operating dentist and probable causes for restoration replacement

Experience (months)	Amalgam, frequency (%)	GIC, frequency (%)	Composite, frequency (%)	Total, frequency (%)	P
Restorative
Up to 36 months	40 (13.99)	11 (3.85)	85 (29.72)	136 (47.55)	0.465
>36 months	43 (15.03)	7 (2.45)	100 (34.97)	150 (52.45)
Total	83 (29.02)	18 (6.29)	185 (64.69)	286 (100.0)
Endodontic
Up to 36 months	8 (7.02)	2 (1.75)	60 (52.63)	70 (61.40)	0.160
>36 months	6 (5.26)	5 (4.39)	33 (28.95)	44 (38.60)
Total	14 (12.28)	7 (6.14)	93 (81.58)	114 (100.0)
Probable causes
Category		Incidence (%)	P
Microleakage		397 (99.25)	0.0001
Bond failure		279 (69.75)
Restoration fatigue		35 (8.75)
Improper tooth preparation		58 (14.50)
Improper proximal contact		96 (24.00)
Insufficient tooth structure		47 (11.75)
Crown not present		102 (25.50)

GIC: Glass-ionomer cement

DISCUSSION

Several factors influence the durability of restorations, including the preparation and size of the restoration, position of the tooth, the restorative material, the clinician’s experience, as well as the patient’s age and gender.

The study found the highest restoration failures in patients aged 31–45 years, while those over 60 showed the least failures. Lifestyle factors such as stress, diet, and irregular dental care contributed to higher risks in younger adults. Furthermore, males have stronger jaw muscles than females due to both physiological differences and lifestyle habits leads to more restoration failure in males which was in accordance with Timothy and Antony.[7] However, Burke et al.[8] analyzed the causes for the placement and replacement of restorations, and when these were correlated with age and gender, no significant association with restoration failure rates was found. In interpreting the present findings, it is important to recognize several potential confounding variables. Age-related lifestyle and caries risk behaviors may have influenced failure rates, particularly in the 31–45 years of age group. Gender-related differences in muscle strength and dietary habits could have contributed to higher failure rates among males. Age, gender, tooth position, occlusal load, oral hygiene, and systemic factors may all be confounders because they can influence both the choice of restoration and the likelihood of failure.

Furthermore, restoration failures were more frequent in mandibular molars due to their exposure to high occlusal forces and the challenges in achieving optimal isolation in this region, resulting in reduced durability of restorative materials. In addition, mandibular molars, particularly those in the lower posterior area, can be more challenging to access during restorative procedures, which can compromise the quality of the placement of restorations.[1] However, Setzer et al.[9] discovered that when factors such as material choice, patient habits, and restoration techniques are controlled, no significant difference was found in the failure rates between mandibular and maxillary molars.

It was analyzed in the present study. Class II tooth preparations had a greater failure rate (67.75%), followed by Class I (26.50%), and the least proportion of failure was seen in Class IV tooth preparations (1.25%). Similarly, a study by Qaiser et al.[10] suggested that the failure rate was higher in proximal lesions (50.8%) than on the occlusal surfaces (18.95%) of tooth preparations, and that smaller restorations demonstrated greater durability compared to larger ones. Furthermore, Shah et al. (2021)[11] found that Class III had lower failure rates. However, a study[12] emphasized that proper cavity preparation, material choice, and technique could significantly affect the success rate of both types of restorations, and advances in bonding agents have significantly reduced the failure rates of Class II tooth preparation.

In this study, most dislodged restorations occurred due to restorative causes (71.5%) rather than endodontic causes (28.5%). This reflects the inherent limitations of restorative materials and techniques, while the structural fragility of ETT further predisposes them to failure and fracture.

Similarly, Opdam et al.[13] described that restorations were liable to developing secondary caries around their margins, especially if there are gaps or poor marginal adaptation, which was a common cause of restorative failure, whereas endodontic treatments, once sealed, are typically more resistant to reinfection as long as the coronal seal remains intact. On contrary, Laske et al.[14] found that restorations placed in ETT and vital teeth had an annual failure rate of 13.4% and 4.9%, respectively.

In the present study, restoration failures were observed most frequently with composites (278), followed by amalgam (97) and GIC (25). Although composites are widely preferred for their esthetics, their longevity is often compromised due to polymerization shrinkage and subsequent marginal gap formation. Forss and Widström[15] reported average survival times of approximately 12 years for amalgam, just under 5 years for composite, and 4 years for GIC, while Bharti et al.[16] highlighted amalgam as the most cost-effective option for posterior direct restorations. Nonetheless, more recent evidence indicates that advancements in composite formulations, bonding systems, and clinical techniques have considerably enhanced their durability.[17]

The study found the highest restoration failures at occlusal sites due to functional stress, followed by distal and mesial sites. Distal failures were linked to access difficulty, larger cavity preparations, and interproximal decay involvement.[18,19]

In addition, Pummer et al.[20] evaluated long-term success of resin composites in 260 patients for a period of 5 years and found that the survival rate for distal–occlusal composite restorations was significantly lower than mesial–occlusal restorations. However, a study conducted by Lygidakis[21] suggested that in some cases, failure rates of restorations may not strictly follow the pattern of occlusal > distal > mesial, depending on the type of restorative material used and the clinical technique.

The study showed that 73.5% of dislodged restorations were associated with secondary caries, which varied significantly among composite, amalgam, and GIC. Composite restorations were most prone due to polymerization shrinkage creating marginal gaps and their rougher surface texture favoring plaque accumulation.

Similarly, Timothy et al. (2021)[7] evaluated 450 restorations and observed secondary caries accounted for more than half of all replacements (51.6%), followed by pain/sensitivity and restoration fracture (15.9%). However, a study by Gordan et al.[22] found that 60% of replacement decisions were due to clinician-perceived defects like marginal staining or fractures, even when secondary caries was not clinically confirmed.

In case of restored and ETT, composite showed more failure rates than silver amalgam and GIC restoration. This could be due to silver amalgam is known for its higher survival rate compared to composite resins and GIC due to its exceptional mechanical properties, resistance to moisture, and ability to withstand masticatory forces over time. Similarly, Bernardo et al.[23] assessed restoration survival over 10 years and found that silver amalgam restorations had better outcomes than composite, especially in large restorations or patients with high caries risk. However, Opdam et al. (2004)[13] found that 17.49% of silver amalgam restorations failed, compared to a lower failure rate of 11.98% for composite restorations, suggesting that composites may offer superior performance in certain cases.

Similarly, Negucioiu et al.[24] found that long years of practice can lead to burnout or fatigue in experienced dentists, which might reduce their concentration, precision, and overall performance.

Analysis of probable causes showed that in vital carious teeth, microleakage (99.25%) was the leading reason for restoration failure, followed by bond failure (69.75%), while in ETT, the absence of crowns (25.5%) and insufficient tooth structure (11.75%) were predominant. Microleakage emerged as a critical factor, as marginal gaps permit bacterial and fluid ingress, leading to secondary caries, progressive tooth damage, and, if undetected, pulpal inflammation or necrosis over time.

Similarly, various studies[25] found that resin-based composite restorations, for instance, are prone to microleakage due to their polymerization shrinkage, which can create a gap between the material and the tooth, allowing for leakage at the margins.

CONCLUSION

Restoration failure rates are influenced by a combination of age-related lifestyle and biological factors, gender-specific habits, and the anatomical and functional characteristics of individual teeth. Among the restorative materials, composite materials showed the highest failure rates.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.