Survival of Partial Laminate Veneers and Categorical Covariates Affecting the Survival: A Systematic Review

3.7.1. Debonding

In the present study, the mean rate of debonding was found as 3,22% per study. During the early days of PLV applications, debonding was accepted as the main failure of this type of restoration [40, 54, 55, 73]. Dunne and Millar [54] reported an 11% debond rate in 1993. Recent articles also reported lower debond rates. In the reviewed literature, four articles reported 0 debond [19, 25, 46, 72]. Six articles reported debond rates under 1% [32, 43, 52, 57, 62, 67]. Nine articles reported a debond rate under 5% but over 1% [23, 24, 27, 28, 35, 42, 60, 63, 65]. Debond rates between 5% and 10% have been reported in seven studies (Table 2) [31, 33, 36, 45, 49-51]. Debonding that does not end but interrupts the PLV service can be recorded as an “event” but may easily be recemented and not reduce the overall survival [33].

3.7.2. Porcelain Fracture

From minute edge cracks to gross fragments, porcelain fractures may occur in varying degrees [27, 42, 62]. In the reviewed literature, porcelain fracture rates were found to be between 0 and 13.05% (Table 2) [19, 23, 25, 27, 28, 31, 32, 36, 38, 39, 42, 44-46, 48, 49, 51, 52, 57, 60, 62, 63, 65, 67, 71]. The present study found the mean fracture rate as 3,65% per study. Porcelain fracture is the main reason for PLV failure, according to Beier et al. [47, 48]. Interaction between porcelain fracture and parafunctions was demonstrated [42, 45, 47]. In contrast with debonded PLvs, porcelain fracture ends the PLV overall survival. Generally, they cannot be repaired, and they should be remade [33]. Minor porcelain and/or enamel chips may break out of PLV restoration. Seven chipping events in the incisal finishing line were reported in 135 PLvs (5,18%) in a follow-up study in 1994 [72]. This rate is lower, as 1.08% and 1.57% in newer reports [23, 67]. Kazakova and Kirov [58] also noted 0.35% chipping in cemented with an acid-etching test group and 0 chipping in cemented with the laser-ablation test group. Chipping does not end or interrupt the service of the PLV but disqualifies the restoration service and esthetic performance.

3.7.3. Tooth Fracture

Tooth fracture is reported as a PLV failure in very few frequencies in the reviewed follow-up articles [32, 33]. D’Arcangelo et al. [32] and Çötert et al. [33] reported tooth fracture rates of 0.27% and 0.5% respectively. They concluded that the fracture incidence of the pulpless teeth was higher, and the difference was significant. Meanwhile, Layton and Walton [52] reported that 6% of the total failures are tooth fractures.

3.7.4. Discoloration

Shade and translucency of the porcelain, resin cement, and substrate tissue and the long-term durability of the color composition, have been mentioned as the factors dominating esthetic success [59]. In 1998, Fradeani reported that the color match of most of the 83 PLV was alpha after 6 years [40]. Similarly, staining of the 135 PLvs has been reported as negligible after 3 years [72]. In contrast, another retrospective study reported color change as the most common PLV failure (20,7%) [29]. In the present study, the mean rate of discoloration was found as 3,77% per study.

3.7.5. Marginal Staining

The thin resin composite cement line between the porcelain and tooth darkens routinely. In the present study, the mean marginal staining rate was found as 12,21% per study. However, the reviewed literature contradicted the marginal staining rate of PLV restorations. This rate was found in reviewed literature as 0 [19, 25, 31, 50], 1.33% [34], 3.4% [43], 4.2% [32], 13.79% [23], 17% [71], 19% [39], 39.30% [51], and 58.6% [29] in different studies (Table 2). Kazakova-Kirov [58] reported that they found less marginal discolorations in laser-ablated PLvs in comparison with acid-etched PLvs. Gresnigt et al. [57] and Beier et al. [47, 48] revealed that the difference in the marginal discoloration rates of the smoker and non-smoker patient groups is statistically significant in favor of non-smokers.

3.7.6. Marginal Disintegration

In the present study, the mean marginal disintegration rate was found as 4,96% per study. Marginal voids or defects were mostly met as small percentages, such as 0.35% [58], 1% [69, 71], 1.25% [70], 2% [51], and 2.5% [32]. However, Gresnigt et al. [23] reported an 18.39% marginal disintegration rate (Table 2). Kazakova and Kirov [58] reported no difference between the marginal disintegration rates of acid-etched and laser-ablated PLvs. In addition, Karagözoğlu et al. [25] reported that the marginal disintegration rate of the minimally prepared PLV group was significantly better than that of the prepless group. Peumans [39] also calculated a 20% marginal disintegration rate and noted that disintegration occurred, especially on existing composites. Guess et al. [35] advocated that the marginal disintegration rates of PLvs increase with extended time.

3.7.7. Gingival Bleeding on Probing

In the present study, the mean gingival bleeding on probing (BOP) rate was 30,76% per study. Gingival and plaque indices have been employed to monitor the gingival health status of PLV restorations for a long time [32], although the score of bleeding in probing has also been used in several studies (Table 2) [30, 32, 50, 71]. Dumfahrt and Schäffer [71] have recorded 25% gingival bleeding in probing. Granell-Ruiz et al. [51] also calculated a 21.6% gingival bleeding in probing. However, at 69%, the rate is much higher, according to Alhekeir et al. [29]. Arif et al. [61] also reported the periodontal health status of 108 PLvs after 198 months. They advocated that 43% of the patients had a normal gingival index, 15% had mild inflammation, and 46% had moderate inflammation and BOP. The pocket depth was found at 2.17% and 2.16% in the upper and lower PLvs, respectively. However, the difference was not significant.

3.7.8. Gingival Recession

The present study found the mean gingival recession rate as 9.93% per study. But in 2000, the 10-year gingival recession rate was 31% [71]. Layton and Walton [52] reported that gingival recession is 12.5% of the total failures of followed PLvs (Table 2). The gingival recession rate was also reported as 0 [29], 2.19% [32], 7.70% [51], and 27% [61].

3.7.9. Hypersensitivity

According to studies regarding PLvs, the absence of hypersensitivity is one of the major advantages of PLvs [55, 72]. Minimal invasive preparation procedures help in minimizing hypersensitivity. Hypersensitivity was reported to be 0 in most PLV follow-up reports [25, 26, 31, 35, 50]. Other articles reported hypersensitivity rates of 3.1% [51], 3.8% [69] and 8.74% [62]. Gresnigt et al. [19, 23] reported a hypersensitivity rate of 17.39% and 21.73%, respectively. Alhekeir et al. [29] also reported a relatively high hypersensitivity rate of 83.30% and attributed this rate to the insufficient skills of the operators (Table 2). The mean rate of hypersensitivity was found as 12,55% per study.

3.7.10. Pulp Necrosis

Although PLvs are performed with minimally invasive conservative preparations, all invasive procedures intervening in the structural unity of the teeth include the risks of vitality change and necrosis of the tooth pulp. Endodontic failures have been reported in very few frequencies such as 0 [19, 23, 25, 26, 35], 0.26% [57], 0.48% [29], 0.61% [65], 2% [27], 2.6% [60] and 2.8% [51]. The present study found the mean pulp necrosis rate as 0,79% per study.

3.8.1. Preparation

Early studies advocated that preparation of the abutment teeth is not compulsory [55, 72]. Recent reports agree that a minimally invasive preparation is required to obtain a suitable space for the restorative material, avoid hypercontour, eliminate the convex contours according to the path of insertion, cover the unesthetic stump color, permit the adjustment check, obtain an internal enamel tissue that can be etched properly, and obtain an atraumatic cervical finishing line [33]. Enamel thickness and age-related changes have been studied, and reparation depth has been reported in 0.3–1.0 mm for normal shaded teeth [70]. However, PLvs with and without abutment preparation have recently been compared, and statistically significant differences have been found regarding marginal and internal gap measurements [25, 62].

3.8.2. Substrate Tissue

The difference between the bonding performances of enamel and dentine tissues has been demonstrated by several retrospective studies (Table 3) [30, 33, 46, 50, 62]. The survival rates of PLvs bonded to enamel and dentine have been reported as 99% and 94%, respectively [46]. The survival rates of PLvs bonded to pure enamel and partially exposed dentine were reported as 93.2% and 95.7%, respectively, and the difference was insignificant [33]. The difference between the survival rates of the PLvs bonded to pure enamel tissue and those bonded to enamel and minimally exposed dentine was found statistically insignificant, while the difference between the survival rates of the PLvs bonded to minimally exposed dentine and those bonded to severely exposed dentine was significant [30]. When dentine exposure is necessary during preparation, enough sound enamel must be protected as much as possible to maintain a good bonding; to obtain maximum bond strength, the preparation margins should be on the sound enamel [33]. Some of the reports reviewed in the present review have considered the outline tissue as a categorical covariate (Table 3) [33, 46]. Gürel et al. [46] calculated the survival rate of the PLvs with preparations confined to the enamel and enamel but only at the margins as 99% and 94%, respectively. They concluded that PLvs have high survival rates when bonded to enamel, providing a safe and predictable treatment option that preserves tooth structure. Çötert et al. [33] calculated the overall survival rates of the PLvs confined on pure enamel, partial enamel, and dentine as 90.5% and 50%, respectively. The Aesthetic Pre-evaluative Temporaries technique has been described to keep the maximum quantity of enamel tissue [50]. Using this approach, 80% of the 580 PLV preparations have been confined to the enamel tissue. Over 144 months, 42 PLvs have failed, but when the preparations were limited to the enamel, the debond rate was reported to decrease to 0 [50]. Preservation of sound enamel tissue can also be maintained by the mock-up technique [22, 46, 59].

3.8.3. Incisal Preparation

Classically, four types of incisal preparations have been described [38]. According to the reviewed literature, with and without overlapped incisal preparations are more popular than the other two [29, 51]. According to a 3-year retrospective report of 135 PLvs without incisal overlapping, debonding was not recorded, while seven incisal chipping events were recorded [72]. Preparation without overlap has been advised as conservative, predictable, and successful. The 2-year survival rates of PLvs with and without overlap have been reported as 85,7% and 94%, respectively, and the difference was found insignificant [30]. In contrast, the 18-month survival rates of PLvs with and without overlap have been reported as 97.8% and 84.7, respectively, and the difference was found to be significant [33]. Guess et al. [31] compared the overlapped PLV with full veneers regarding overall survival and failures and found insignificant differences. Beier et al. [49] also compared the overall survival of overlapped and non-overlapped veneers after 60, 96, 120, 180, and 240 months and reported that the differences were statistically significant. Smales and Etemadi [38] also reported that the difference between overlapped and non-overlapped veneer survival rates is insignificant (Table 3).

3.8.4. Proximal Preparation

Preparation of the proximal chamfers is recommended in teeth with normal proximal contacts. In contrast, in diastema cases, proximal surfaces may require feathering [33]. Survival rates of the PLvs with chamfered and feathered proximal outlines were reported as 96.3% and 87.4%, respectively, and the difference was found to be significant (Table 3) [33].

3.8.5. Gingival Finishing Level

Creation of a mini-chamfer finishing line at the gingival margin level or above it has been advised, and the negative influence of the infra gingival finishing level on PLV survival has been demonstrated [33]. Survival rates of the PLvs finishing at supra and infra gingival levels were calculated as 99.4 and 63.3%, respectively, and the difference was found to be significant (Table 3) [33].

3.8.6. Vitality

A significantly higher failure risk of the non-vital PLV abutments compared with the vital ones was demonstrated (Table 3) [33, 47, 48, 57].

3.8.7. Existing Restorations

Recent studies showed that existing composite restorations may not be required to be replaced prior to the cementation of PLvs when the carious lesion is absent (Table 3) [23, 46, 57]. No significant influence of the presence of composite restorations was reported on the failure rates of the followed PLvs [46]. In addition, the survival rates of the PLvs luted to the intact teeth and the PLvs luted to the teeth with existing restorations were reported as 96% and 93.5%, respectively, and the difference was found statistically insignificant [23]. Therefore, an existing composite restoration of good quality is not required to be removed, but it is better to be surface-treated by silica coating and silanization prior to the luting of the PLV restoration [57].

3.8.8. Location

The overall survival rates of the upper and lower PLvs were found as 97.5% and 95%, respectively, and the difference was found significant [33], while mouth quadrant differences were found insignificant in another study [21, 67].

3.8.9. Veneer Material

Awan et al. [41] reported the overall survival of the ceramo-metal restorations and PLvs applied to the endodontically treated and discolored teeth as 78.26% and 63.15%, respectively, and the difference was found to be insignificant. Indirect veneers are made of several materials, including acrylic, composite, and various porcelain materials. The survival rates of the heat-pressed and CAD-CAMed veneers were found to be both 100% [22]. The overall survival of EmpressCAD and EMaxCAD veneers was reported as 97.80% and 100%, respectively, and the difference was found to be significant [44]. The overall survival of CAD-CAMed (Cerec) PLvs was calculated as 94%, and 98% of the survived restorations were classified as clinically acceptable after 9 years [60]. The authors advocated that the high survival rate and favorable clinical results would support the use of CAD-CAMed PLvs in clinical situations similar to those for laboratory-processed porcelain veneers (Table 3). Veneers of the anterior and posterior regions, made of veneered and monolithic lithium disilicate (LiDiSi) were followed for 42 months, and the survival rates were found to be 98% and 100%, respectively, and the difference was found to be insignificant [67].

The survival and clinical performances of porcelain and indirect composite laminate veneers were compared [19]. Three failures in the group of resin composite veneers were reported, but the difference between the survival rates was found to be insignificant. Minor voids and defects were observed in six of the composite veneers and three of the ceramic veneers. Slight staining at the margins (n = 3) and slightly rough surfaces were more frequently observed for the resin composite laminate veneers (n = 18) up to the final recall (Table 3). In another study comparing resin and porcelain veneers, the overall survival was 75% and 100%, respectively, and the difference was significant [64].

3.8.10. Luting Material and Technique

PLvs must be bonded with a correct adhesive technique to reach a successful survival rate [37]. Reviewed literature showed that the resin composite luting agents have been preferred for PLvs [19, 23, 29, 33, 34, 45, 62, 72]. A light-cured composite luting agent was preferred in a 7-year retrospective study [32]. The clinical performance of the PLvs cemented with light-cured hybrid composite (Z100, 3M-ESPE) to the teeth treated with total-etch adhesive (Scotchbond Multi-Purpose Plus, 3M-ESPE) and self-etch adhesive (AdheSE, Ivoclar-Vivadent) systems were compared. A statistically significant difference between the total-etch and self-etch groups was not found [34] (Table 3).

3.8.11. Extensions

PLvs may be used to extend tooth contours in any direction [46]. The effects of proximal, apical, or incisal extensions on PLV survival have been studied in the literature. It was shown that extensions in the incisal direction can increase the failure probability 2–3 times, while the extensions in the apical direction do not create any failure risk (Table 3) [46]. Malchiodi et al. [24] also reported that the difference between the survival rates of extended and non-extended veneers was insignificant.

3.8.12. Parafunctions

Parafunctions, mostly bruxism, may potentially affect the PLvs and other dental restorations [45]. The risk of failure was calculated as 7.7 times greater when associated with an existing parafunction (Table 3) [47, 48]. The survival rates of the PLvs of bruxist and non-bruxist patients were compared according to the presence or absence of ceramic failures such as cracks, fractures, and debonding [45]. It was concluded that bruxism activity should be recognized as a higher risk of failure in PLV applications (Table 3). Survival rates of the PLvs applied to bruxist patients were found to be 89.1% in the splint-wearer group and 63.9% in the non-splint-wearer group, respectively; the difference was significant [42].

3.8.13. Tobacco Consumption

The success rates of PLvs of smokers and non-smokers were compared, and a significantly greater marginal discoloration in the PLvs of the smoker patients was noticed [29, 43, 47, 48, 57, 59, 64].

3.8.14. Operator Skills and Expertise

Burke and Lucarotti [20] considered the factors associated with the need for re-intervention of teeth restored with PLvs. They scanned the data of 2562 PLvs in 1177 patients and collected the factors influencing PLV survival. They concluded that dentist factors did not appear to influence PLV survival after re-intervention. Rocha et al. [62] reported that operator skills and experience did not influence the survival of PLV. However, some of the papers reviewed in the present study indicated the influence of the skills and experience of the operator on the clinical performance of PLvs (Table 3) [29, 55].