Assessment of resin -ceramic bond strength under various pH conditions for different ceramic materials subjected to two surface treatment protocols

Statement of the problem: The 2 step ceramic surface treatment “ HF acid etching followed by silane application” has been used for years to secure an efficient bond between ceramics and resin cements, however the urge for simplification and making the bonding procedure less technique sensitive have pushed the dentists to shift to one step ceramic surface treatment “self etch ceramic primer”. Although studies proved their reliability, till now there is no data available on their effect on bond stability in different pH conditions
Purpose: The aim of the current study was to evaluate microshear bond strength between resin and different ceramic materials (e.max, VITA ENAMIC and VITA SUPPRINITY) preatreated with two different protocols (2 step and 1 step) after being subjected to various pH storage media
Materials and Methods: A total of ninety ceramic discs were fabricated in this study from CAD/CAM blocks. The discs were divided into three groups according to ceramic material as follows; Group 1: Thirty discs constructed from lithium disilicate glass ceramic (e.max CAD), Group 2: Thirty discs constructed from polymer infiltrated ceramic- network material (VITA ENAMIC) and Group 3: Thirty discs constructed from Zirconia-lithium silicate glass-ceramic materials (VITA SUPRINITY). Each of the previous groups were further subdivided into two equal subgroups according to the surface treatment protocol used as follows; Subgroup 1: fifteen discs were treated with 2 step bonding protocol (etched with hydrofluoric acid followed by silane application) and Subgroup 2: fifteen discs were treated with 1 step application of self etching primer (Monobond etch and prime). The two subgroups were again equally divided (5 each) and assigned to one of the three storage solutions with different pHs : acidic, neutral and alkaline media.Ceramic discs were obtained by sectioning the CAD/CAM blocks using Isomat 1000 followed by crystallization of the e.max and VITA SUPPRINITY discs. For first subgroup, the ceramic discs were subjected to two step surface treatment protocol consisting of hydroflouric acid etching, rinsing followed by silane application. While the second subgroup was subjected to surface treament using one
step monobond etch and prime protocol. For both subgroups,each ceramic substrate was then prepared to receive 5 resin microtubules. Five samples of each ceramic resin assembly subgroup was then randomly selected and designated in one of the following storage media for a period of seven days:1) Cola solution representing acidic medium having pH value of 2.5. 2) Distilled water representing neutral medium having pH value of 7 3) Licorice solution representing alkaline medium having pH value of 8.4. At the end of the storage period,micro shear bond strength test was performed to debond the specimens in a universal testing machine (Model 3345; Instron Industrial Products, Norwood, MA, USA) with a crosshead speed of 0.5 mm/s. The maximum load at failure was recorded in Newtons (N) unit and was divided over the bonded area (mm2) to convert to MPa unit. Data was then collected, tabulated and statistically analyzed.
Results: With acidic pH: in e.max CAD and VITA ENAMIC groups; it was found that two steps surface treatment approach recorded statistically significant higher mean microshear bond strength value than one step approach as proven by paired t-test (P<0.05), while for VITA SUPRINITY group; it was found that two steps surface treatment approach recorded statistically non-significant higher mean microshear bond strength value than one step approach as demonstrated by paired t-test (P= 0.1945> 0.05). With neutral pH: in e.max CAD and VITA ENAMIC groups; it was found that two steps surface treatment approach recorded statistically non significant higher mean microshear bond strength value than one step approach as proven by paired t-test (P>0.05), while for VITA SUPRINITY group; it was found that two steps surface treatment approach recorded statistically significant higher mean microshear bond strength value than one step approach as demonstrated by paired t-test (P= 0.03<0.05)With alkaline pH: : in e.max CAD and VITA ENAMIC groups; it was found that two steps surface treatment approach recorded statistically significant higher mean microshear bond strength value than one step approach as proven by paired t-test (P<0.05), while for VITA SUPRINITY group; it was found that two steps surface treatment approach recorded statistically non-significant higher mean microshear bond strength value than one step approach as demonstrated by paired t-test (P= 0.2121> 0.05)
Conclusions: Within the limitations of this study, the following conclusions and clinical recommendations could be advised:1) Although microshear bond strength of the two step etch and prime surface treatment protocol was significantly higher than that of one step self-etching ceramic primer protocol,however the values for all tested materials under various Ph conditions were nearly within a clinically acceptable range, thus it could be suggested that self etching primers can be safely used without affecting clinical performance of the restorations. 2) In patients subjected to predominately acidic or alkaline oral pH environments, both surface treatment protocols can be safely used when VITA SUPPRINITY restorations are indicated, however when VITA ENAMIC or e.max CAD are used, it is recommended to use the two step surface treatment protocol to ensure more stable bond strength 3) In patients having a neutral balanced oral pH environment, both surface treatment protocols can be safely used when VITA ENAMIC or e.max CAD restorations are used, however when VITA SUPPRINITY is recommended, it is advisable to use the two step surface treatment protocol to yield better ceramic resin bond durability. 4) Generally speaking, VITA ENAMIC restorations combined with one step self etching primer are not recommended for patients having acidic pH oral media as it yielded the lowest bond strength values between all subgroups