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Endo Tribune Middle East & Africa Edition No. 2, 2017

PUBLISHED IN DUBAI www.dental-tribune.me March-April 2017 | No. 2, Vol. 7 Exploring the fracture resistance of retentive pin-retained e.max press onlays in molars By Dr. Les Kalman & Yasmin Joseph, Canada Retentive titanium dentinal pins have been combined with indirect restorations. Application of pins has been used with lithium disilicate, an indirect pressed ceramic restora- tive material, termed e.max. The objective of this study was to inves- tigate the fracture resistance of pin- retained versus non pin-retained in- direct e.max press restorations. Ten human extracted teeth were used for the control and ten for the test group. Titanium dentinal pins were placed and e.max press restorations were fabricated, by a commercial lab- oratory, and then cemented. Fracture resistance was assessed. Data was collected and results were obtained. Fracture resistance of both groups indicated no signifi cant difference in values. An observation from test- ing illuminated that pin-reinforced e.max benefi tted from a controlled fracture, which minimized tooth damage. The data suggests that pin-reinforced indirect e.max resto- rations offer no appreciable differ- ence in fracture resistance. Further testing would be required to expand upon the sample size, explore other strength vectors and consider a clini- cal in vestigation. Introduction The loss of tooth structure, from disease or biomechanical stress, requires the replacement of tooth structure through dental restora- tion techniques. This may occur ei- ther directly or indirectly. Extensive tooth restorations typically require indirect restorations.[1] Indirect den- tal restorations benefi t from excel- lent form, function, esthetics, and strength; however, the retention of indirect restorations can prove prob- lematic.[1] This is primarily due to variable technique-sensitive chemi- cal bond of the restorative material with the tooth.[2] The type of resto- ration used largely depends on the magnitude of tooth destruction and dictates unique preparation design characteristics.[3] With the increasing demand in es- thetics, use of ceramics has become more prevalent in restorative den- tistry.[4] E.max, a ceramic and metal- free restorative material, has been demonstrated to be an extremely strong, dependable restoration with ideal esthetics.[2] It is a highly bio- compatible glass ceramic composed of lithium disilicate.[5] E.max is also among the most durable dental ma- terials to date.[6] Previous studies have concluded that e.max poses no health risk to dental patients and has little potential to cause irritation or sensitizing reactions, when com- pared to composite or gold restora- tions.[2] Although the primary retention of an indirect restoration is based on bond strength, secondary elements can be introduced to further increase surface area and retentive strength, such as pins.[7] Traditionally, reten- tive pins were employed to offer sig- nifi cant retention to direct restora- tions when minimal tooth structure remained.[8] Effective utilization of pins required proper application of biomechanical principles in each clinical case.[9] Adequate dentin, to support the pin, remains an im- portant factor in the evaluation of the clinical success of retentive res- torations.[10] The type of pin used also determines the success rate of the restoration. Among the two pin types, titanium retentive pins have been found to be highly biocompat- ibility with minimal corrosive activ- ity.[10] Due to the sensitivity of indirect restoration bonding and result- ant retention, an investigation on Control Group (N) 3016 2277 2121 3079 2510 2258 3120 2396 2859 2222 Test Group (N) 2679 2436 1605 2606 1716 2927 3060 1575 3118 2385 Table 1: Fracture resistance values for samples (Newtons) Fig. 1: No pin onlay tooth preparation Fig. 2: Pin onlay tooth preparation Fig. 3: Periapical radiograph verifying pin placement Fig. 4: Occlusal view of e.max press onlay restoration whether the use of titanium reten- tive pins would offer an increase in fracture resistance seemed fi tting. If there was a signifi cant increase in fracture resistance between the re- storative material and the tooth, pin reinforced e.max press restorations could justify further investigation. In addition, with advances in 3-D intra- oral imaging and CAD/CAM, a digital work fl ow would provide a simple and predictable clinical alternative. Materials and methods Human extracted molar teeth were used for this investigation. They were sorted and randomized. A to- tal of 20 extracted molar teeth were used. The control group contained ten molar teeth. Each tooth was prepared for a four surface onlay restoration which did not incorpo- rate pins. The test group included ten molar teeth. Each tooth was pre- pared for a four surface onlay res- toration which did not incorporate pins. Each four surface e.max onlay restoration preparation had either the buccal or lingual wall remain- ing intact (Fig. 1) following standard pin-retained amalgam guidelines. [11] Titanium pins with a diameter of 0.6 mm were used (Stabilok; Fairfax Dental Inc.). Two pins were placed in each tooth at the appropriate line angles; pin 1 was placed on the me- sial side whereas pin 2 was placed on the distal side of each molar tooth (Fig. 2). Pins were inserted to a 2 mm depth. The top 1mm was sheared off and smoothed.[8] Pin length was slightly variable among the teeth. Radiographs were taken in a buc- colingual and mesiodistal fashion to verify pin placement (Fig. 3). All tooth specimens were packaged and sealed in a moisture controlled con- tainer and shipped to a dental labo- ratory (DentUSA) for restoration fab- rication with e.max press (IPS e.max Press; Ivoclar Vivadent). Specimens were returned in the same manner along with the e.max onlay restora- tions (Figs. 4 & 5). Tooth specimens and restorations were prepared and bonded (Fig. 6) using Multilink adhe- sive cementation system (Multilink Automix; Ivoclar Vivadent) follow- ing manufacturing recommenda- tions.[12] Cement fl ash was removed and the restorations were polished following standard Schulich Dentistry proto- cols. The prepared tooth was fi xed with ortho resin (Fig. 7) (acrylic resin, DENTSPLY Caulk) in the stabiliza- tion ring (Fig. 8). A universal loading machine (Instron laboratory test- ing unit: ITW) was utilized to apply an axial load to the tooth until the tooth fractured (Fig. 9). The machine applied pressure at a maximum crosshead speed of 0.5 mm/min. Tooth fracture was assessed visually and measured in Newtons for all the teeth in the control and test groups (Fig. 10). Results The force (Newtons) required to cause fracture of either the restora- tion or tooth, or a combination of the two, was extremely variable (Table 1). The test group suggested greater variability among the values and the highest fracture resistance value. There was no signifi cant difference ÿPage A2

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