Can a chin implant slightly pull the mentalis muscle upwards? Possible?

A portion of the mentalis muscle is detached when a chin implant is placed. Usually the implant sits on the lowest part of the chin and the remainder of the mentalis muscle is unaffected. The soft tissue of the chin is pushed horizontally and not vertically to any significant degree. It may be possible to reduce some of the bulk of the chin pad from a submental incision and thereby pull the chin soft tissue downward in order to reduce the appearance of any chin scars. 

That would take a specially designed chin implant that has a superior ledge to it to create that soft tissue effect. Whether such an immediate effect is sustained as the soft tissues relax over time is another revenant question.

 Hi, when the mentalis (chin muscle) is ptotic (weak dn sagging) adding forward projection with a chin implant can cause upward rotation of the sagging muscle.  This would however, happen much less in a muscle that isn't sagged.  In either case, this would "not" have the same effect as stretching the skin over the chin (improving appearance of chin scars).  Chin implants, as described below, are used to correct weak chins.  I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut segments of bone).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone. 
Hope this helps.