Fixed V - Lec 5 & 6 - Resin Bonded Retainers .pdf

Resin Bonded Retainers Adhesive Bridges “ Maryland Bridges FPD 515 Prof. Jylan Elguindy  Definition Advantages Disadvantages Indications Contraindications Types  ILOs 1-Identify proper case selection for resin bonded bridge RBB 2-Recognize...

Resin Bonded Retainers Adhesive Bridges “ Maryland Bridges FPD 515 Prof. Jylan Elguindy  Definition Advantages Disadvantages Indications Contraindications Types  ILOs 1-Identify proper case selection for resin bonded bridge RBB 2-Recognize preparation features 3-Select proper surface treatment 4-List causes of failure of RBB  Definition It is a single pontic supported by thin metallic retainers placed lingually and proximally on the abutment teeth. The preparation is limited to enamel and the labial surface remains intact.  Advantages: - Conservative preparation; as the preparation should be confined to tooth enamel only. - Tissue tolerant; supragingival margins. - Less traumatic preparation; so potential for pulpal trauma is minimized. - Esthetic advantages; as the labial surface of abutments is left intact. - Easy impression making. - Anesthesi is often unnece ssary. - a restorations are not required. - Provisional & Re-bonding is possible - Reduced cost. Reduced chair side time  Disadvantages: - Questionable longevity; debonding rates increase with time and are related to prep design, luting agent selection and the area of placement within the dental arch. - Posterior and mandibular areas have higher dislodgement rates; which might be due to increased occlusal forces and isolation difficulty during cementation. - Cannot restore badly broken down teeth. - Grayness problem; in thin translucent teeth ( with metallic resin bonded retainers not with ceramic RBB). - No space & contour correction. - Enamel modifications are required - No alignment correction. - Usually is restricted to single pontic (except missing 2 lower central incisors ).  Indications 1. Replacement of congenitally missing tooth or teeth lost by traumatic injuries especially in young patients. 2. usually used for the replacement of missing anterior teeth in children & adolescents. Since conventional prosthesis is contraindicated in young patients because of management problems, inadequate plaque control and large size of the pulps. Maxillary incisor replacement; one or two can be replaced in an open-bite, edge-to-edge occlusion 3. restricted to single pontic (except missing 2 lower central incisors ). 4. Short span and in case of open bite 5. Single posterior tooth replacement. 6. Significant crown length. occluso-gingival height of teeth (2-3 mm vertical friction to axial walls) for adequate surface area for bonding 7.Unrestored & Caries-free abutment abutment 8.Abutment with sufficient amount of enamel for etching. 9.Medically compromised and adolescent patients 10.Splinting of periodontally compromised teeth. 11. Stabilizing dentition after orthodontic treatment. 12. Excellent moisture control  Contraindications: 1. Lack of sufficient enamel; as it causes lack of retention.( cases of hypoplasia, demineralization) 2. very thin or translucent anterior teeth; as it causes grayness problem. 3.unaesthetic abutment teeth. 4.Abutments with short clinical crowns, extensively restored and damaged ones. 5. long edentulous spans as it produces greater stresses to casting and the adhesive bond 6. Edentulous spaces that need adjustment. 7. Deep vertical overlap; as it might need to remove so much enamel from the lingual surface of maxillary incisors to have clearance, thereby endangering retention. 8. Nickel sensitivity; as most are Ni-Cr restorations. 9. Space problems as diastema  Contraindications: 10.Para-functional habits? Bruxism? Deep-bite? place excessive forces on the resin-retained bridge & the resistance to displacement of these retainers is lower than in conventional FDPs Metallic Fiber RBB reinforced All RBB ceramic RBB  FABRICATION In the fabrication of resin-bonded FDPs, attention to details in the following 3 phases is necessary for predictable success 1. Preparation of the abutment teeth. 2. Design of the restoration. 3. Bonding  General Principles of successful resin bonded retainers Design 1Creating a distinct path of insertion by modifications to the enamel contours , of the abutment teeth. 2 When seated, the restoration should not be displaced in any direction by occlusal forces. Resistance features as shallow grooves within enamel 3-The framework design must limit the stresses placed on the luting cement and the bonded interface. The only way to prevent stress fatigue of the resin is to obtain a retentive framework with one path of insertion. 4Axial reduction and guide planes on the proximal surface with a faciolingual lock. 5Maximum coverage of virginal enamel.180o wrap around to enhance retention to lingual displacement and provide maximum bonding area. 6- 1mm supragingival finish line. Occlusal clearance of 0.5mm. 7-Vertical stops as cingulum rest on canine or flat counter sinks on the incisors and occlusal rests on posterior teeth which will aid in preventing horizontal and vertical displacement  Anterior design principles  lingual clearance Armamentarium : football or wheel stone Sufficient lingual surface clearance 0.6 to 0.8 mm for occlusion. (Additional 0.2 mm to accommodate protrusive movement ) Lingual reduction will stop 1.5-2 mm from the incisal edge or just incisal to the incisal most incisal contact Cingulum : is reduced parallel to path of insertion Finish line Chamfer finish line is supra gingival ( 0.3-0.5) thickness placed supragingivally (1mm above gingival crest)  Cingulum rest Armamentarium : inverted cone or fissure bur Resistance form as vertical stops against occlusal forces to resist gingival displacement ( counter sink ). - Proximal reduction on the surface adjacent to the edentulous area and extending slightly facially but stop before the facio- proximal line angle. - Reduction extends to the other proximal surface and stops just short of the proximal contact.( No opening of proximal contact) - Supragingival chamfer finish line. - Resistance features by two grooves; one on each side of the proximal surface. (grooves 0.75 mm wide & 0.5 mm depth) resist displacement in the buccolingual direction  Proximal surface : proximo labial extensions with out metal display ( stop before line angle) Additional means of retention : created by proximal grooves to resist lingual displacement should be placed slightly lingual to the labial termination of the proximal reduction No wrap around (why?) but it is substituted by proximal grooves and cingulum rest No opening of proximal contact Armamentarium : Taper carbide bur  Vertical stops Slight supra- Gingival chamfer F.L 0.5 mm inter - 0.5 mm deep occlusal proximal grooves clearance parallel to each F.L adjacent to the edentulous other space placed labially as far as possible  Preparation of mandibular anterior teeth is similar to that for the maxillary incisors. Lingual enamel thickness is 11% to 50% less than for maxillary teeth, and tooth preparation must therefore be more conservative Posterior tooth preparation Design of Posterior Resin Bonded Fixed Partial Dentures retainer retain ponti er c 4 4 5 7 Occlusal Occlusal mesial & rests Narrow rests distal pontic mesial & Note maximal wrap  Design of Posterior Resin Bonded Fixed Partial Dentures The basic framework for the posterior resin-bonded FDP consists of three major components: The occlusal rest resistance to gingival displacement. The retentive surface resistance to occlusal displacement. The proximal wrap resistance to torqueing forces.  Lingual axial reduction at the height of contour about 0.5- 0.8 mm Armamentarium : tapered stone with round end.  Mandibular molars : The lingual wall of the mandibular tooth prepared in a single plane Maxillary molars : requires a two-plane reduction because of occlusal function and the taper of these functional cusps in the occlusal two thirds  Finish line Chamfer finish line (0.3-0.5 mm )1mm away from gingival margin (supra gingivally ) Inter proximal finish line knife-edge margin is better for avoiding enamel penetration.  180 degree wrap around extend buccally beyond the distobuccal line angle in mesial abutment and mesio buccal line angle in distal abutment to Enhance resistance to lingual displacement & increase enamel surface area for bonding The proximal walls must be parallel to each other or with slight taper. Mesial Distal  Proximal grooves Armamentarium : fissure bur 0.5 mm depth to resist torquing forces Standard : 2 grooves must be parallel to each other one near the facio proximal angle adjacent to the edentulous space and one at the opposite to lingoproximal corner with 180 degree of axial wall coverage.  Occlusal Seat Extend on the cuspal slope of lingual cusp  The preparation for a mandibular first premolar different from that for other premolar preparations. Because the placement of a rest seat would leave very little solid tooth structure in the small lingual cusp. so coverage of the entire small lingual cusp is recommended  Occlusal rest Armamentarium : carbide – diamond inverted cone bur. resistance form as vertical stops to resist gingival displacement ( counter sink ) and direct forces from the pontic to the center of the abutment tooth.  1mm deep occlusal rests inclined toward the center of the abutment teeth (will act as a vertical stop).One rest seat at the marginal ridge adjacent to the edentulous area. Second occlusal rest may be placed on the opposite side.  If there is an existing amalgam, all of the amalgam or at least all of its surfaces is removed so that box form can be utilized. The entire occlusal outline of the existing amalgam restoration is included within the outline of the retainer's occlusal rest.  Single-abutment Two-abutments cantilever RBB RBB a b Single-abutment metal-framed, resin-bonded bridges with - no preparation (a) for the replacement of missing lateral incisors, -and tooth preparation (b) replacing an upper left second premolar  Design for posterior teeth - Lingual axial reduction at the height of contour - 1mm deep occlusal rests. - 180o wraparound. - Proximal resistance by grooves. - A distinct path of insertion by parallelism - Supragingival chamfer finish line.  Summary Design For Anterior Teeth - Mark the centric occlusal contact. - Ensure occlusal clearance of 0.5mm. - Lingual reduction will stop 1.5-2mm from the incisal edge or just incisal to the incisal most occlusal contact, whichever closer to the incisal edge. - Cingulum rest or flat counter sinks on the lingual surface. - Additional 0.2mm clearance to accommodate protrusive movements. - Proximal reduction on the surface adjacent to the edentulous area and extending slightly facial but stop before the facio- proximal line angle. - Reduction extends to the other proximal surface and stops just short of the proximal contact. - Supragingival chamfer finish line. - Resistance features by two grooves; one on each side of the proximal surface.  Types of Adhesion: I. Mechanical Adhesion: Two adherends (surfaces) mechanically interlock together forming an ATTACHMENT at the interface. II.Chemical Adhesion: Chemical bonding between two substances TRUE ADHESION which is stronger than mechanical. Attachment is Composed of: 1-Etched Enamel Surface. 2- Bonding Resin. 3- Treated Metal or Ceramic wings  Bonding of Resin Bonded Retainers The attachment is composed of: 1. Etched enamel surface 2. Surface treated metal surface/ceramic 3. Bonding resin Surface treatment of the metal To improve retention by: Mechanical methods 1-Macro Mechanical 2-Micro Mechanical Chemical methods 1-Interfacial 2-Adhesive Rosenstiel, Land, Fujimoto. Contemporary fixed prosthodontics  Surface Treatment techniques: 1. Rochette Bridge 2. Mechanical Beads.. Macro- I 3. Cast Mesh :Duralingual System mechanical 4. Virginia Bridge (Soluble Salt Technique). Bonding: 1. Air Abrasion: sandblasting II. 2. Maryland Bridge in 1982 (Electrolytic etching) Micromechanica 3. Chemical etching l Bonding: 4. Porous metal coating III. A. Interfacial bonding: Adhesive B. Adhesive bonding: Chemical bonding:  Mechanical bonding Macromechanical Micromechanical 1.Cast perforated RBB 1.Electrolytic Etching (Rochette) (Maryland Bridge) 2.Water soluble salt 2. Chemical etching crystals (Virginia B) 3. Porous Metal Coating 3. Cast Mesh Pattern 4. Sandblasting (Duralingual) 4.Retention Acrylic Beads  Macro Mechanical 1 Cast perforated resin retainer (Rochette bridge) Used with noble and base metal alloy Alain Rochette in 1973 introduced this type of bridge. It is created by perforating cast metal to get mechanical interlocking with the resin To prevent weakening of the framework- Too large and too closely placed perforations should be avoided. The perforations should be approximately 1 mm apart and have a maximum diameter of 1.5mm  Disadvantages 1 Weakening of metal by perforation. 2 Resin exposed to wear in oral cavity 3Resin exposed to stress at area of perforation 4-Retention is limited to perforated areas.  II. Water soluble salt crystals (Virginia Bridge) Used with noble and base metal alloy Incorporation of salt crystals (150-250 microns) in the fitting surface of pattern leaving 0.5 mm at the margin The pattern is washed before investing to dissolve the crystals leaving voids that present in final casting Disadvantages: - It provides weaker bond than etched ones.  3-Cast Mesh Pattern (Dura Lingual) Used with noble and base metal alloys It is done by applying A moldable net like nylon mesh on the die on which the wax or resin pattern is build. then the wax pattern is cast with the mesh producing a mesh like surface when the restoration is cast. Advantages: Greater bond strength with the resin cement than the etched surface. Disadvantage: 1) Wax may blockout the undercuts 2)Technique sensitive. 3) The castings are thicker lingually Can’t be tolerated by the patient.  4 Retentive Acrylic Beads Used with noble and base metal alloys Acrylic resin beads with diameter of 0.2_0.3mm is attached to the fitting surface of the pattern before casting result in macro roughness in the fitting surface of final restoration This old method failed due to considerable restoration thickness  1.Mechanical Bonding b. Micromechanical Bonding I. Electrolytic Etching (Maryland Bridge) - Ni-Cr Beryllium alloys are etched with sulfuric acid. - Ni-Cr without Beryllium and Co-Cr alloys are etched with nitric acid. - The etching cycle is 3 min in 10% sulfuric with a current 300 M amps/cm3. - porosity is created in the fitting surface of the metal by differential Electromechanical etching. Tech. Procedure: -The polished surface of the frame work is covered with wax then submerged in electrolytic etching unit containing Etching acid. - The treated fitting surface should NOT be touched till cementation  Advantages - Improved retention - Thinner retainers, but resist flexing - Highly polished castings Disadvantages - Time consuming - Technique sensitive - Limited to base metal alloys - Any contamination will lead to failure  II. Chemical Etching base metal alloys Using a gel of nitric and hydrochloric acids for 20 min. used only with base metal Alloys Advantages 1-Simple and more reliable in comparison to Electrolytic Etching. 2- Restorations can be Re-etched in case of failure. III. Porous Metal Coating Firing very fine particles of stainless steel powder to the fitting surface of the metal frame work Creating a porous metal surface coating that provides an increase in surface area for the retention of resin. It is used for both noble and base metal alloys  IV. Sandblasting Used with noble and base metal alloy Using 250 um alumina powder for 30 sec. then washed in ultrasonic cleaner and distilled water. it has a large effect on the quality of the metal-resin bond through producing a clean surface with roughness. The increased area of the micro-roughness metal also activate the surface formation of chemical bonds. Advantages Sandblasting → micro porosities (micro mechechanical retention) →↑ surface area. → ↑ wettability by increasing surface reactivity of the alloys. DISADVANTAGE insufficient for long term bonding.  Chemical bonding Interfacial bonding Adhesive bonding I. Deposition of Tin layer 1. Heating the alloy 1. Electrolytic Tin-plating 2. Immersion in 2. Ion sputtering technique oxidizing solution 3.Application of a Liquid 3.Immersion in conc. Ga-Sn alloy (adlloy) nitric acid II.Deposition of silica layer 4. Silicoater/ Pyrosil pen 5. Rocatec/Cojet  2. Chemical Bonding a. Interfacial bonding It relies on an intermediate layer as Tin layer , that is fused to the metal framework and can bond to the resin cement so there is no direct contact between metal and resin.  I. Electrolytic Tin-plating: It is used with noble alloys. It is performed following sandblasting of the casting, to adhere small Tin crystals A layer of tin of 0.2-0.4μm is needed to form a chemical bond. The cements bond to the oxide layer which develops on the tin-plated surface. Tin-plating in which direct current is used to deposit Tin from an amide solution II. Ion Coating surface treatment Using ion sputtering technique, which is used to deposit thin films of a material onto a substrate. By creating accelerated ions to strike a Tin target, causing emission of atoms or molecules from the target in a straight line, which is deposited on the substrate; giving a tin oxide surface. It bonds adhesive resins to noble and base metal alloys.  III. Application of a Liquid Ga-Sn alloy (adlloy) Leading to the formation of a new alloy layer containing Ga & Sn on the adherent alloy surface. The adlloy is a mixture of solid Sn & liquid (90% Ga & 10% Sn). It bonds 4-META adhesive resin to noble alloys. Advantages - High bond strength for noble alloys - Easy application - Takes short time Pyrochemical silica coating It is based on using elevated temperatures to deposit silica. It is used with base metal and noble alloys.  IV. Silicoater Technique - Silicoater technique by which the sandblasted casting pass through a special flame (150-200 oC). Then a coating solution is injected and results in a silica- carbon layer coating of 0.1-1 µm thickness layer. The coating solution contains tetraethoxysilane (TEOS). Then when the silica-coated surface is cooled to room temperature, it is silanized with silane coupling agent that bond chemically to resin cement used with noble and base metal alloys.  A modification of the silicoater technology is the extra-oral use of a hand-piece named Silano-pen or Pyrosil pen. Disadvantages : Expensive Uneven distribution of flame Chemically unstable silica layers  V. Rocatec System - Tribochemical surface conditioning of the casting by silica coating. The system uses a three-step laboratory procedure. The casting surface is first air-abraded with 120 um Al2O3 particles to remove contaminants and provide microroughness. Then, the surface is air-abraded with a silica-coated Al2O3 particles 30 µm size, accelerated with compressed air, which impact the casting surface, with a resultant heat reaching 1200 oC, to establish the tribochemical coating of a silicon-dioxide layer embedded in the surface of the substrate. Finally, the casting surface is silanized and is ready for bonding with resin luting agent.  Cojet system Another system employs a two-step chairside procedure that tribochemically coats the casting surface by air abrading it with a silica-modified Al2O3 particles before silanization.  2.Chemical Bonding b. Adhesive Bonding It relies on chemically reactive groups within resin cements to bond directly to the oxide layer on the alloy. I. Heating the alloy (noble alloys) Heating the gold alloy that contains copper will form a copper rich layer that bond chemically to resin cement The strong bond formed is attributed to the copper rich deposit that is formed on the alloy surface by heating. 4-META resin cement is used for bonding.  II. Immersion in an oxidizing solution used for base metal alloys - The oxidizing solution is composed of: 3% weight aqueous sulphuric acid with 1% weight potassium permanganate. - Metal is sandblasted with alumina, immersed in oxidizing solution for 2 min, washed in distilled water, then dried. III. Immersion in concentrated nitric acid Immersion of Ni-Cr alloy will form an oxide film that will adhere to 4-META in resin cement.  All ceramic resin bonded bridges Advantages: 1. The major advantage of all-ceramic, resin-bonded bridges over metal-framed, resin-bonded bridges is their esthetic potential. 2. all-ceramic materials offer advantages of increased biocompatibility and lower plaque accumulation.  All ceramic resin bonded bridges Disadvantages of conventional resin bonded bridges 1. Grey shimmer of the metal wings through the abutment teeth 2. Higher corrosion rate 3. Allergenic potential of the non-precious alloys used Moustafa Maher  All ceramic RBB high strength non-etchable ceramics as zirconia is the ceramic of choice. Surface treatment of Ceramics -In case of Zirconia, the fitting surface is treated by sandblasting or Rocatec system as the Zirconia is Un-etchable. - Manufacturers have developed a primer for Zirconia, un-etchable ceramics & metals to bond with the resin cement. - Z-Prime Plus : enhance bond strength to zirconia , Alumina & metal with resin cement due to its unique composition of : - MDP phosphate monomer -Research supports the fact that MDP phosphate monomers contribute to long-term bonding to Zirconia, while Silane does not contribute to zirconia adhesion.  Surface conditioning Conditioning can be defined as ttt of a surface to increase its critical surface energy for adhesion. If the surface tension of a liquid is less than the surface energy of a substrate, the contact angle will be “0” and liquid will spread on the substrate Conditioning is either with silanes or primers  Silane coupling agents their organofunctional group polymerize with hydrophobic resin-composite monomers, while the hydrolyzable inorganic groups bond with hydrophilic inorganic hydroxyl- rich (-OH) surfaces, which are the silica and silica-coated surfaces. Several reports supported the use of Phosphate-based Primers in bonding Zr.  Surface treatment of tooth structure: 1. Acid etching technique: -Tooth is cleaned with pumice, washed and dried. -Then etched with 37 % phosphoric acid for 30 sec, washed and dried. 2. Laser etch technique: -Tooth is cleaned with pumice, isolated and dried -Laser initiator is applied. -Then tooth is etched with laser for 60 sec. -Excess initiator is then removed, and tooth is washed and dried.  Bonding Resin: 1. Conventional resin cement: It is a modified unfilled/filled composite resin with a thin film thickness. 2. Adhesive resin cement: Which rely on adhesion to the metal and not on microretention features in the surface of metal for its bond strength ( as Panavia and 4META). Panavia is a filled Bis-GMA composite resin with a phosphate ester monomer. It bonds well to sandblasted base metal alloys and tin plated noble alloys. The powder contains 75% quartz filler and is insoluble in oral fluids. The cement shows excellent bond strengths to sandblasted base-metal alloys' and tin- plated noble alloys. Panavia possesses a unique anaerobic setting characteristic. It will not set in the presence of oxygen. To ensure complete polymerization , an oxyguard (polyethylene glycol gel) should be placed over the restoration margins. This creates an oxygen barrier, and can be washed away after the material has completely set  Panavia 21 Panavia was the first commercial product that contained MDP( 10-methacryloyloxydecyl dihydrogen phosphate ) in the liquid which leads to high /long bond strength PANAVIA 21 is suitable for a broad range of indications and is available in the 3 color shades EX (white), TC (tooth color) and OP (opaque). Self-etching, self-curing primer for reduced post-op sensitivity. Low or absence of microleakage. cement contain phosphate based monomer that have ability to etch and chemically bond to tooth structure. fluoride releasing cement Radiopaque Low film thickness and low solubility Panavia is anaerobic cement (does not set in presence of oxygen ) oxyguard II gel acts as oxygen barrier  Panavia 21 adhesive resin cement Panavia 21 exhibits excellent bond strength with base metal alloys and tin plated noble metals The latest version of this luting agent is both chemically and light cured; as an alternative to the gel, a curing light can be used to polymerize the margins Panavia 21 is supplied in opaque and tooth-colored (TC) form This allows the application of opaque to the lingual aspect of an anterior retainer and the translucent tooth color to the inter proximal aspect so that an opaque line is not visible from the facial aspect This method makes it possible to mask the unesthetic metallic gray retainer, thus preventing it from showing through translucent enamel  Step-by-step procedure with Panavia 21 resin adhesive cement 1 Isolate abutments with rubber dam Clean the teeth with pumice and — water 2acid etch with 37%phosphoric acid for 30 seconds Rinse, dry , and maintain air drying until the primer is applied. 3 At this time the mix of Panavia 21 cement is prepared and set it aside till — application 4 Application of Panavia ED Primer to the etched enamel surface — 5 Dry the Panavia ED Primer to ensure evaporation of the solvent (this should — remain on the enamel surface for 30 seconds before drying) — (Although Panavia ED Primer is a self etch primer it is should not be used without enamel etching because bonded retainer surfaces are not “freshly prepared enamel.” After preparation, they acquire a salivary pellicle, which limits the self-etching capabilities of this type of product — 6-Apply the premixed Panavia 21 cement (both opaque and tooth-colored if it is an anterior retainer) to the inner surface of the casting 7Seat the casting firmly, and maintain pressure while removing the excess resin cement with a brush. The cement sets within 60 to 90 seconds under the casting but not at the margins, which are exposed to air 8 Light-cure the margins or apply Oxyguard II to exclude air 9Rinse away Oxyguard II after 2 minutes, and remove residual cement with a sharp hand instrument 10 Major finishing, polishing, and occlusal adjustments should be performed before the restoration is bonded  Causes of Failure of Resin Bonded Retainers Improper patient selection: a) Gender: Although it is known that masticatory forces are stronger in men than in women , gender does not seem to affect the longevity of RBFPD b) Parafunctional habits: Parafunctional habits and occlusal interference have been associated with higher debonding rates. Bruxism is considered a stress factor that causes premature failure of RBFPDs. c)Span length: Resin bonded is restricted to only single tooth missing. increasing the number of pontics will significantly decrease the longevity d) Existing old restoration or caries. In case of anterior teeth class III old composite restoration should be replaced with fresh composite to promote good adhesion with resin cement. In case of large class IV caries or old composite the prognosis will be questionable if resin bonded restoration is selected. it is more advisable to use full coverage restoration to ensure long term clinical performance e)Improper teeth alignment (poor path of insertion) f)Insufficient vertical length of the abutment g)Insufficient enamel for bonding. ) Improper alloysselection: Because of the high modulus of elasticity, base metal alloys such as Nickel chromium or Cobalt-Chromium are preferred to gold alloys. Improper tooth preparation a) Insufficient lingual & proximal reduction b) Incomplete 180º wrap-around extension. c) Lack of proximal grooves. d) Lack of accommodation to mandibular excursion (protrusion).  Failure of bonding procedure 1. Contamination. 2. Inappropriate luting cement. 3. Incorrect manipulation of cement. Knowledge Never Ends