Sciascia was not charged with killing Hineteaorangi as police determined the cause of her death could not be proven.
Whānau - some supporting Sciascia and some not - filled the courtroom as he was sentenced by Judge Bridget Mackintosh.
Among them was Hineteaorangi's mother, who is still in a relationship with Sciascia, with whom she recently had a new baby.
Before court proceedings began, Judge Mackintosh addressed the room, acknowledging the grief, sadness, anger, loss, frustration, and disappointment felt by all.
A letter of apology from Sciascia was handed up to Judge Mackintosh by his lawyer Eric Forster, who also started by acknowledging those present.
He said Sciascia's letter was "sincere" in its remorse, advocating for discounts to be offered because of it, and his one guilty plea.
Forster said cultural reasons such as deprivation from a young age should also be considered.
"I hope at some point there might be some healing," he said.
Crown prosecutor Steve Manning said there were a number of cumulative factors to be considered in sentencing, including Hineteaorangi's young age and vulnerability, the breach of trust, and the "extent of force and nature of the injury".
Reading excerpts from victim impact statements, Judge Mackintosh said the family had spoken of the "torment" suffered and their difficulty in managing feelings of loss.
They also spoke of the difficulty of reconciling these with their feelings about Sciascia.
Sciascia himself was described as "devastated" by the loss of Hineteaorangi.
"I can sense the overwhelming sense of grief, sadness and anger at what happened."
Adopting a sentence starting point four-and-a-half years jail, Judge Mackintosh said the extent of force used indicated how culpable Sciascia was and how serious the offending was.
"It is clear to me [...] that there was significant force required to cause the fracture of the skull."
She cited the serious breach of trust, vulnerability of Hineteaorangi, and nature of the "extremely serious" injuries as aggravating factors.
She also noted it had occurred on the back of other offending and was "not a one-off situation" - the two assault charges relating to Sciascia hitting her with a cellphone on her head a few days prior to her death, on October 3 and 4, 2019.
She acknowledged mitigating factors laid out in the cultural report and imposed a sentence of four years and three months' jail, with a two-year minimum non-parole period.
In a statement issued after sentencing, police expressed their deep sadness at the case.
"While nothing will be able to bring Hineteaorangi back, we are hopeful the arrest and prosecution of Sciascia provides some comfort for her loved ones.
"No child should be the victim of violence, and the horrendous abuse inflicted on children by those who are supposed to protect them is unforgivable.
"We acknowledge the deep grief felt by her family and we continue to provide support to them as best we can as they come to terms with the sentencing."