This
retrospective evaluation assessed the clinical performance of posterior CAD/CAM
ceramic endocrowns and examined how residual tooth tissue and other clinical
parameters influenced failure rates. Endocrowns demonstrated high success and
survival-89.1 % and 95.7 %, respectively-over a mean follow-up of 15 months,
regardless of classification, material, or tooth type. However, the hypothesis
that all parameters would be non-influential was only partially supported,
since plaque index emerged as a significant predictor of failure (p < 0.01).
Advances in adhesive protocols and reinforced ceramics have shifted restorative
strategies toward more conservative options for ETT, such as endocrowns,
onlays, and overlays, which preserve more tooth structure than traditional
post–core crowns [27]. Preserving residual tooth structure is critical for
biomechanical integrity and reduces fracture risk [23,28], so we specifically
investigated whether classification by remaining tooth walls correlated with clinical
outcomes. Despite limited failures and consequently modest statistical power,
binary logistic regression revealed no significant effect of restoration class
on failure. This aligns with Belleflamme et al and Taha et al. who also found
no link between tooth-remnant thickness and clinical performance when proper
preparation and isolation protocols are followed [23,29]. In contrast, some in
vitro studies report increased fracture strength with greater occlusal
thickness, suggesting that the relationship between residual structure and
longevity remains unresolved and warrants further research with larger cohorts
and longer follow-up (30-32). Our success rate mirrors those of previous
clinical investigations [21,23,27]. Belleflamme et al. reported an 89.9 %
success rate after 10 years of clinical service and Su-Ning Hu et al. observed
a 92 % success over 1–3 years [23,27]. The favorable short-term outcomes likely
reflect the monoblock design of endocrowns, which reduces interfaces and stress
concentrations compared with multi-component post–core systems [1,8]. Debonding
was the most common failure mode, accounting for 40 % of failures, consistent
with Govare et al. (2). Endocrown retention depends on macro mechanical
engagement in the pulp chamber and adhesive bonding at cavity margins. [16].
Overextending preparation can compromise marginal adaptation [33], yet studies
show no fatigue resistance difference between 2 mm and 4 mm pulp-chamber depths
[34]. Fortunately, debonded restorations can typically be re-cemented, making
this failure non-catastrophic [2,35]. When restorations were grouped into
lithiumdisilicate-based and leucite-based ceramics, material type did not
significantly influence failure rates. This agrees with Hasanzade et al. [36]
and Rigolin et al. [37], who reported similar marginal adaptation and survival
for both materials. Although Belleflamme et al. noted a lower fracture rate for
pressed lithium disilicate compared with leucite ceramics [23], our use of
CAD/CAM ceramics may account for equivalent performance. Lithium disilicate
remains the preferred material for its reliable bond to resin cements and
long-term stability [38]. Emerging materials such as polyetherketoneketone
(PEKK) also show promise; preliminary studies suggest PEKK endocrowns offer
superior performance due to their mechanical properties and favorable stress
distribution [40], but clinical validation is needed. Tooth type -molar versus
premolar- also had no significant effect on failure rates in our study,
although evidence in the literature is mixed. Several investigations favor
molar endocrowns, citing premolars’ higher lever arm forces and non-axial
loading as risk factors [2,35,41], while Otto et al. and Thomas et al. found no
difference [42,43]. Given that fewer premolars meet stringent endocrown
indications, future studies should specifically address premolar restorations
and their unique biomechanical challenges.
Occlusal
risk factors including temporomandibular disorders, bruxism, and facet wear
showed no significant associations with failure, likely due to uneven
distribution and the limited event rate. Larger, more balanced cohorts are
required to clarify these relationships. The finding that plaque index is a
strong predictor of endocrown failure underscores the critical role of oral
hygiene. Each one-unit increase in plaque index multiplied the odds of failure
by 36, possibly because increased microbial load at the dentin cement interface
promotes acid production that undermines adhesion and leads to deboning. All debonded
restorations in this study occurred in patients with a plaque index score of 1.
Accordingly, clinicians should emphasize rigorous plaque control and schedule
closer follow-up for patients with elevated plaque scores. Future research
should investigate whether enhanced hygiene protocols can reduce failure rates.
This study’s retrospective, single-center design introduces inherent
biases—selection bias from including only documented follow-up cases,
information bias from reliance on clinical records, heterogeneity in follow-up
duration, and limited external validity due to the small number of failures.
Examiner calibration, strict inclusion criteria, standardized FDI outcome
measures, and multivariable regression helped mitigate these concerns, but residual
confounding may persist. Additionally, the single follow-up per restoration
precluded time-to-event analysis; prospective studies with scheduled serial
assessments and Kaplan Meier analysis are recommended to validate and extend
these findings.